Structure of the histone mRNA hairpin required for cell cycle regulation of histone gene expression.

Expression of replication-dependent histone genes requires a conserved hairpin RNA element in the 3' untranslated regions of poly(A)-less histone mRNAs. The 3' hairpin element is recognized by the hairpin-binding protein or stem-loop-binding protein (HBP/SLBP). This protein-RNA interaction is important for the endonucleolytic cleavage generating the mature mRNA 3' end. The 3' hairpin and presumably HBP/SLBP are also required for nucleocytoplasmic transport, translation, and stability of histone mRNAs. RNA 3' processing and mRNA stability are both regulated during the cell cycle. Here, we have determined the three-dimensional structure of a 24-mer RNA comprising a mammalian histone RNA hairpin using heteronuclear multidimensional NMR spectroscopy. The hairpin adopts a novel UUUC tetraloop conformation that is stabilized by base stacking involving the first and third loop uridines and a closing U-A base pair, and by hydrogen bonding between the first and third uridines in the tetraloop. The HBP interaction of hairpin RNA variants was analyzed in band shift experiments. Particularly important interactions for HBP recognition are mediated by the closing U-A base pair and the first and third loop uridines, whose Watson-Crick functional groups are exposed towards the major groove of the RNA hairpin. The results obtained provide novel structural insight into the interaction of the histone 3' hairpin with HBP, and thus the regulation of histone mRNA metabolism.

Growth Cone Localization of the mRNA Encoding the Chromatin Regulator HMGN5 Modulates Neurite Outgrowth

Neurons exploit local mRNA translation and retrograde transport of transcription factors to regulate gene expression in response to signaling events at distal neuronal ends. Whether epigenetic factors could also be involved in such regulation is not known. We report that the mRNA encoding the high-mobility group N5 (HMGN5) chromatin binding protein localizes to growth cones of both neuron-like cells and of hippocampal neurons, where it has the potential to be translated, and that HMGN5 can be retrogradely transported into the nucleus along neurites. Loss of HMGN5 function induces transcriptional changes and impairs neurite outgrowth, while HMGN5 overexpression induces neurite outgrowth and chromatin decompaction; these effects are dependent on growth cone localization of Hmgn5 mRNA. We suggest that the localization and local translation of transcripts coding for epigenetic factors couple the dynamic neuronal outgrowth process with chromatin regulation in the nucleus.

Mechanisms by which nonsense codons downregulate T-cell receptor transcripts

Nonsense-mediated mRNA decay (NMD) is a quality control mechanism that degrades aberrant mRNAs harboring premature termination codons (PTCs). Two out of three T-cell receptor β (TCRβ) transcripts carry PTCs as a result of error-prone programmed rearrangements that occur at this locus during lymphocyte maturation. PTCs decrease TCRβ mRNA levels to a much greater extent than mRNAs transcribed from non-rearranging genes. This robust decrease in TCRβ mRNA levels is not a unique characteristic of the T-cell environment or the TCRβ promoter. The simplest explanation for this is that PTC-bearing TCRβ mRNAs elicit a stronger NMD response. An alternative explanation is NMD collaborates with another mechanism to dramatically decrease PTC-bearing TCRβ mRNA levels. ^ In my dissertation, I investigated the molecular mechanism behind the strong decrease in TCRβ mRNA levels triggered by PTCs. To determine the location of this response, I performed mRNA half-life analysis and found that PTCs elicited more rapid TCRβ mRNA decay in the nuclear fraction, not the cytoplasmic fraction. Although decay was restricted to the nuclear fraction, PTC-bearing TCRβ transcript levels were extremely low in the cytoplasm, a phenomenon that I named the nonsense-codon induced partitioning shift (NIPS). I established that NIPS shares several qualities with NMD, including its dependence on translation and NMD factors. Several lines of evidence suggested that NIPS results from PTCs eliciting retention of TCRβ transcripts in the nuclear fraction. This retention, as well as rapid TCRβ mRNA decay, most likely occurs in either the nucleoplasm or the outer nuclear membrane, based on analysis of nuclear and cytoplasmic markers in the highly purified nuclei I used for my studies. To further address the location of decay, I asked whether nuclear or cytoplasmic RNA decay factors mediated the destruction of PTC-bearing mRNAs. My results suggested that a nuclear component of the 3'-to-5' exosome, as well as an endonucleolytic activity, are involved in the destruction of PTC-containing TCRβ mRNAs. Individual endogenous NMD substrates had differential requirements for nuclear and cytoplasmic exonucleases. In summary, my results provide evidence that PTCs trigger multiple mechanisms involving multiple decay factors to remove and regulate mRNAs in mammalian cells. ^

Rifaximin-mediated changes to the epithelial cell proteome: 2-D gel analysis

Diarrhea remains a significant cause of worldwide morbidity and mortality. Over 4 million children die of diarrhea annually. Although antibiotics can be used as prophylaxis or for treatment of diarrhea, concern remains over antibiotic resistance. Rifaximin is a semi-synthetic rifamycin derivative that can be used to treat symptoms of infectious diarrhea, inflammatory bowel syndrome, bacterial overgrowth of the small bowel, pouchitis, and fulminant ulcerative colitis. Rifaximin is of particular interest because it is poorly adsorbed in the intestines, shows no indication of inducing bacterial resistance, and has minimal effect on intestinal flora. In order to better understand how rifaximin functions, we sought to compare the protein expression profile of cells pretreated with rifaximin, as compared to cells treated with acetone, rifamycin (control antibiotic), or media (untreated). 2-D gel electrophoresis identified 38 protein spots that were up- or down-regulated by over 2-fold in rifaximin treated cells compared to controls. 16 of these spots were down-regulated, including keratin, annexin A5, intestinal-type alkaline phosphatase, histone h4, and histone-binding protein RbbP4. 22 spots were up-regulated, including heat shock protein HSP 90 alpha, alkaline phosphatase, and fascin. Many of the identified proteins are associated with cell structure and cytoskeleton, transcription and translation, and cellular metabolism. A better understanding of the functionality of rifaximin will identify additional potential uses for rifaximin and determine for whom the drug is best suited. ^

Traducciones, versiones y homenajes en la poesía de José Emilio Pacheco

La importancia de la traducción y de la versión en la actividad intelectual del escritor mexicano José Emilio Pacheco (1939) cobra mayor relevancia en cuanto ambas constituyeron la sección final de sus poemarios, con el título de 'Aproximaciones'. Por otra parte, todos sus libros acuden a fuertes relaciones intertextuales, homenajes, citas y textos 'a la manera de', además del uso de heterónomos, conformando una red que respalda su concepción de que 'la poesía se hace entre todos, concepción que le posibilita, por momentos, confiar en la permanencia de la palabra poética ante la convicción del futuro como destrucción y ruina

Traducciones, versiones y homenajes en la poesía de José Emilio Pacheco

La importancia de la traducción y de la versión en la actividad intelectual del escritor mexicano José Emilio Pacheco (1939) cobra mayor relevancia en cuanto ambas constituyeron la sección final de sus poemarios, con el título de 'Aproximaciones'. Por otra parte, todos sus libros acuden a fuertes relaciones intertextuales, homenajes, citas y textos 'a la manera de', además del uso de heterónomos, conformando una red que respalda su concepción de que 'la poesía se hace entre todos, concepción que le posibilita, por momentos, confiar en la permanencia de la palabra poética ante la convicción del futuro como destrucción y ruina

Traducciones, versiones y homenajes en la poesía de José Emilio Pacheco

La importancia de la traducción y de la versión en la actividad intelectual del escritor mexicano José Emilio Pacheco (1939) cobra mayor relevancia en cuanto ambas constituyeron la sección final de sus poemarios, con el título de 'Aproximaciones'. Por otra parte, todos sus libros acuden a fuertes relaciones intertextuales, homenajes, citas y textos 'a la manera de', además del uso de heterónomos, conformando una red que respalda su concepción de que 'la poesía se hace entre todos, concepción que le posibilita, por momentos, confiar en la permanencia de la palabra poética ante la convicción del futuro como destrucción y ruina

Arquitectura de información para medicion de rendimiento en entornos e-manufacturing

La implantación de las tecnologías Internet ha permitido la extensión del uso de estrategias e-manufacturing y el desarrollo de herramientas para la recopilación, transformación y sincronización de datos de fabricación vía web. En este ámbito, un área de potencial desarrollo es la extensión del virtual manufacturing a los procesos de Performance Management (PM), área crítica para la toma de decisiones y ejecución de acciones de mejora en fabricación. Este trabajo doctoral propone un Arquitectura de Información para el desarrollo de herramientas virtuales en el ámbito PM. Su aplicación permite asegurar la interoperabilidad necesaria en los procesos de tratamiento de información de toma de decisión. Está formado por tres sub-sistemas: un modelo conceptual, un modelo de objetos y un marco Web compuesto de una plataforma de información y una arquitectura de servicios Web (WS). El modelo conceptual y el modelo de objetos se basa en el desarrollo de toda la información que se necesita para definir y obtener los diferentes indicadores de medida que requieren los procesos PM. La plataforma de información hace uso de las tecnologías XML y B2MML para estructurar un nuevo conjunto de esquemas de mensajes de intercambio de medición de rendimiento (PMXML). Esta plataforma de información se complementa con una arquitectura de servicios web que hace uso de estos esquemas para integrar los procesos de codificación, decodificación, traducción y evaluación de los performance key indicators (KPI). Estos servicios realizan todas las transacciones que permiten transformar los datos origen en información inteligente usable en los procesos de toma de decisión. Un caso práctico de intercambio de datos en procesos de medición del área de mantenimiento de equipos es mostrado para verificar la utilidad de la arquitectura. ABSTRAC The implementation of Internet technologies has led to e-Manufacturing technologies becoming more widely used and to the development of tools for compiling, transforming and synchronizing manufacturing data through the Web. In this context, a potential area for development is the extension of virtual manufacturing to Performance Measurement (PM) processes, a critical area for decision-making and implementing improvement actions in manufacturing. This thesis proposes a Information Architecture to integrate decision support systems in e-manufacturing. Specifically, the proposed architecture offers a homogeneous PM information exchange model that can be applied trough decision support in emanufacturing environment. Its application improves the necessary interoperability in decision-making data processing tasks. It comprises three sub-systems: a data model, a object model and Web Framework which is composed by a PM information platform and PM-Web services architecture. . The data model and the object model are based on developing all the information required to define and acquire the different indicators required by PM processes. The PM information platform uses XML and B2MML technologies to structure a new set of performance measurement exchange message schemas (PM-XML). This PM information platform is complemented by a PM-Web Services architecture that uses these schemas to integrate the coding, decoding, translation and assessment processes of the key performance indicators (KPIs). These services perform all the transactions that enable the source data to be transformed into smart data that can be used in the decision-making processes. A practical example of data exchange for measurement processes in the area of equipment maintenance is shown to demonstrate the utility of the architecture.

Automatic motion compensation of free breathing acquired myocardial perfusion data by using independent component analysis

Images acquired during free breathing using first-pass gadolinium-enhanced myocardial perfusion magnetic resonance imaging (MRI) exhibit a quasiperiodic motion pattern that needs to be compensated for if a further automatic analysis of the perfusion is to be executed. In this work, we present a method to compensate this movement by combining independent component analysis (ICA) and image registration: First, we use ICA and a time?frequency analysis to identify the motion and separate it from the intensity change induced by the contrast agent. Then, synthetic reference images are created by recombining all the independent components but the one related to the motion. Therefore, the resulting image series does not exhibit motion and its images have intensities similar to those of their original counterparts. Motion compensation is then achieved by using a multi-pass image registration procedure. We tested our method on 39 image series acquired from 13 patients, covering the basal, mid and apical areas of the left heart ventricle and consisting of 58 perfusion images each. We validated our method by comparing manually tracked intensity profiles of the myocardial sections to automatically generated ones before and after registration of 13 patient data sets (39 distinct slices). We compared linear, non-linear, and combined ICA based registration approaches and previously published motion compensation schemes. Considering run-time and accuracy, a two-step ICA based motion compensation scheme that first optimizes a translation and then for non-linear transformation performed best and achieves registration of the whole series in 32 ± 12 s on a recent workstation. The proposed scheme improves the Pearsons correlation coefficient between manually and automatically obtained time?intensity curves from .84 ± .19 before registration to .96 ± .06 after registration

Image analysis by moment invariants using a set of step-like basis functions

Moment invariants have been thoroughly studied and repeatedly proposed as one of the most powerful tools for 2D shape identification. In this paper a set of such descriptors is proposed, being the basis functions discontinuous in a finite number of points. The goal of using discontinuous functions is to avoid the Gibbs phenomenon, and therefore to yield a better approximation capability for discontinuous signals, as images. Moreover, the proposed set of moments allows the definition of rotation invariants, being this the other main design concern. Translation and scale invariance are achieved by means of standard image normalization. Tests are conducted to evaluate the behavior of these descriptors in noisy environments, where images are corrupted with Gaussian noise up to different SNR values. Results are compared to those obtained using Zernike moments, showing that the proposed descriptor has the same performance in image retrieval tasks in noisy environments, but demanding much less computational power for every stage in the query chain.

Autonomous Landing of an Unmanned Aerial Vehicle using Image-Based Fuzzy Control

This paper presents a vision based autonomous landing control approach for unmanned aerial vehicles (UAV). The 3D position of an unmanned helicopter is estimated based on the homographies estimated of a known landmark. The translation and altitude estimation of the helicopter against the helipad position are the only information that is used to control the longitudinal, lateral and descend speeds of the vehicle. The control system approach consists in three Fuzzy controllers to manage the speeds of each 3D axis of the aircraft s coordinate system. The 3D position estimation was proven rst, comparing it with the GPS + IMU data with very good results. The robust of the vision algorithm against occlusions was also tested. The excellent behavior of the Fuzzy control approach using the 3D position estimation based in homographies was proved in an outdoors test using a real unmanned helicopter.

Multilingual number transcription for text-to-speech conversion

This paper describes the text normalization module of a text to speech fully-trainable conversion system and its application to number transcription. The main target is to generate a language independent text normalization module, based on data instead of on expert rules. This paper proposes a general architecture based on statistical machine translation techniques. This proposal is composed of three main modules: a tokenizer for splitting the text input into a token graph, a phrase-based translation module for token translation, and a post-processing module for removing some tokens. This architecture has been evaluated for number transcription in several languages: English, Spanish and Romanian. Number transcription is an important aspect in the text normalization problem.

New methods for the synthesis of radiation patterns of coupled antenna arrays = Nuevos métodos de síntesis de diagramas de radiación de agrupaciones de antenas acopladas

El principal objetivo de esta tesis es el desarrollo de métodos de síntesis de diagramas de radiación de agrupaciones de antenas, en donde se realiza una caracterización electromagnética rigurosa de los elementos radiantes y de los acoplos mutuos existentes. Esta caracterización no se realiza habitualmente en la gran mayoría de métodos de síntesis encontrados en la literatura, debido fundamentalmente a dos razones. Por un lado, se considera que el diagrama de radiación de un array de antenas se puede aproximar con el factor de array que únicamente tiene en cuenta la posición de los elementos y las excitaciones aplicadas a los mismos. Sin embargo, como se mostrará en esta tesis, en múltiples ocasiones un riguroso análisis de los elementos radiantes y del acoplo mutuo entre ellos es importante ya que los resultados obtenidos pueden ser notablemente diferentes. Por otro lado, no es sencillo combinar un método de análisis electromagnético con un proceso de síntesis de diagramas de radiación. Los métodos de análisis de agrupaciones de antenas suelen ser costosos computacionalmente, ya que son estructuras grandes en términos de longitudes de onda. Generalmente, un diseño de un problema electromagnético suele comprender varios análisis de la estructura, dependiendo de las variaciones de las características, lo que hace este proceso muy costoso. Dos métodos se utilizan en esta tesis para el análisis de los arrays acoplados. Ambos están basados en el método de los elementos finitos, la descomposición de dominio y el análisis modal para analizar la estructura radiante y han sido desarrollados en el grupo de investigación donde se engloba esta tesis. El primero de ellos es una técnica de análisis de arrays finitos basado en la aproximación de array infinito. Su uso es indicado para arrays planos de grandes dimensiones con elementos equiespaciados. El segundo caracteriza el array y el acoplo mutuo entre elementos a partir de una expansión en modos esféricos del campo radiado por cada uno de los elementos. Este método calcula los acoplos entre los diferentes elementos del array usando las propiedades de traslación y rotación de los modos esféricos. Es capaz de analizar agrupaciones de elementos distribuidos de forma arbitraria. Ambas técnicas utilizan una formulación matricial que caracteriza de forma rigurosa el campo radiado por el array. Esto las hace muy apropiadas para su posterior uso en una herramienta de diseño, como los métodos de síntesis desarrollados en esta tesis. Los resultados obtenidos por estas técnicas de síntesis, que incluyen métodos rigurosos de análisis, son consecuentemente más precisos. La síntesis de arrays consiste en modificar uno o varios parámetros de las agrupaciones de antenas buscando unas determinadas especificaciones de las características de radiación. Los parámetros utilizados como variables de optimización pueden ser varios. Los más utilizados son las excitaciones aplicadas a los elementos, pero también es posible modificar otros parámetros de diseño como son las posiciones de los elementos o las rotaciones de estos. Los objetivos de las síntesis pueden ser dirigir el haz o haces en una determinada dirección o conformar el haz con formas arbitrarias. Además, es posible minimizar el nivel de los lóbulos secundarios o del rizado en las regiones deseadas, imponer nulos que evitan posibles interferencias o reducir el nivel de la componente contrapolar. El método para el análisis de arrays finitos basado en la aproximación de array infinito considera un array finito como un array infinito con un número finito de elementos excitados. Los elementos no excitados están físicamente presentes y pueden presentar tres diferentes terminaciones, corto-circuito, circuito abierto y adaptados. Cada una de estas terminaciones simulará mejor el entorno real en el que el array se encuentre. Este método de análisis se integra en la tesis con dos métodos diferentes de síntesis de diagramas de radiación. En el primero de ellos se presenta un método basado en programación lineal en donde es posible dirigir el haz o haces, en la dirección deseada, además de ejercer un control sobre los lóbulos secundarios o imponer nulos. Este método es muy eficiente y obtiene soluciones óptimas. El mismo método de análisis es también aplicado a un método de conformación de haz, en donde un problema originalmente no convexo (y de difícil solución) es transformado en un problema convexo imponiendo restricciones de simetría, resolviendo de este modo eficientemente un problema complejo. Con este método es posible diseñar diagramas de radiación con haces de forma arbitraria, ejerciendo un control en el rizado del lóbulo principal, así como en el nivel de los lóbulos secundarios. El método de análisis de arrays basado en la expansión en modos esféricos se integra en la tesis con tres técnicas de síntesis de diagramas de radiación. Se propone inicialmente una síntesis de conformación del haz basado en el método de la recuperación de fase resuelta de forma iterativa mediante métodos convexos, en donde relajando las restricciones del problema original se consiguen unas soluciones cercanas a las óptimas de manera eficiente. Dos métodos de síntesis se han propuesto, donde las variables de optimización son las posiciones y las rotaciones de los elementos respectivamente. Se define una función de coste basada en la intensidad de radiación, la cual es minimizada de forma iterativa con el método del gradiente. Ambos métodos reducen el nivel de los lóbulos secundarios minimizando una función de coste. El gradiente de la función de coste es obtenido en términos de la variable de optimización en cada método. Esta función de coste está formada por la expresión rigurosa de la intensidad de radiación y por una función de peso definida por el usuario para imponer prioridades sobre las diferentes regiones de radiación, si así se desea. Por último, se presenta un método en el cual, mediante técnicas de programación entera, se buscan las fases discretas que generan un diagrama de radiación lo más cercano posible al deseado. Con este método se obtienen diseños que minimizan el coste de fabricación. En cada uno de las diferentes técnicas propuestas en la tesis, se presentan resultados con elementos reales que muestran las capacidades y posibilidades que los métodos ofrecen. Se comparan los resultados con otros métodos disponibles en la literatura. Se muestra la importancia de tener en cuenta los diagramas de los elementos reales y los acoplos mutuos en el proceso de síntesis y se comparan los resultados obtenidos con herramientas de software comerciales. ABSTRACT The main objective of this thesis is the development of optimization methods for the radiation pattern synthesis of array antennas in which a rigorous electromagnetic characterization of the radiators and the mutual coupling between them is performed. The electromagnetic characterization is usually overlooked in most of the available synthesis methods in the literature, this is mainly due to two reasons. On the one hand, it is argued that the radiation pattern of an array is mainly influenced by the array factor and that the mutual coupling plays a minor role. As it is shown in this thesis, the mutual coupling and the rigorous characterization of the array antenna influences significantly in the array performance and its computation leads to differences in the results obtained. On the other hand, it is difficult to introduce an analysis procedure into a synthesis technique. The analysis of array antennas is generally expensive computationally as the structure to analyze is large in terms of wavelengths. A synthesis method requires to carry out a large number of analysis, this makes the synthesis problem very expensive computationally or intractable in some cases. Two methods have been used in this thesis for the analysis of coupled antenna arrays, both of them have been developed in the research group in which this thesis is involved. They are based on the finite element method (FEM), the domain decomposition and the modal analysis. The first one obtains a finite array characterization with the results obtained from the infinite array approach. It is specially indicated for the analysis of large arrays with equispaced elements. The second one characterizes the array elements and the mutual coupling between them with a spherical wave expansion of the radiated field by each element. The mutual coupling is computed using the properties of translation and rotation of spherical waves. This method is able to analyze arrays with elements placed on an arbitrary distribution. Both techniques provide a matrix formulation that makes them very suitable for being integrated in synthesis techniques, the results obtained from these synthesis methods will be very accurate. The array synthesis stands for the modification of one or several array parameters looking for some desired specifications of the radiation pattern. The array parameters used as optimization variables are usually the excitation weights applied to the array elements, but some other array characteristics can be used as well, such as the array elements positions or rotations. The desired specifications may be to steer the beam towards any specific direction or to generate shaped beams with arbitrary geometry. Further characteristics can be handled as well, such as minimize the side lobe level in some other radiating regions, to minimize the ripple of the shaped beam, to take control over the cross-polar component or to impose nulls on the radiation pattern to avoid possible interferences from specific directions. The analysis method based on the infinite array approach considers an infinite array with a finite number of excited elements. The infinite non-excited elements are physically present and may have three different terminations, short-circuit, open circuit and match terminated. Each of this terminations is a better simulation for the real environment of the array. This method is used in this thesis for the development of two synthesis methods. In the first one, a multi-objective radiation pattern synthesis is presented, in which it is possible to steer the beam or beams in desired directions, minimizing the side lobe level and with the possibility of imposing nulls in the radiation pattern. This method is very efficient and obtains optimal solutions as it is based on convex programming. The same analysis method is used in a shaped beam technique in which an originally non-convex problem is transformed into a convex one applying symmetry restrictions, thus solving a complex problem in an efficient way. This method allows the synthesis of shaped beam radiation patterns controlling the ripple in the mainlobe and the side lobe level. The analysis method based on the spherical wave expansion is applied for different synthesis techniques of the radiation pattern of coupled arrays. A shaped beam synthesis is presented, in which a convex formulation is proposed based on the phase retrieval method. In this technique, an originally non-convex problem is solved using a relaxation and solving a convex problems iteratively. Two methods are proposed based on the gradient method. A cost function is defined involving the radiation intensity of the coupled array and a weighting function that provides more degrees of freedom to the designer. The gradient of the cost function is computed with respect to the positions in one of them and the rotations of the elements in the second one. The elements are moved or rotated iteratively following the results of the gradient. A highly non-convex problem is solved very efficiently, obtaining very good results that are dependent on the starting point. Finally, an optimization method is presented where discrete digital phases are synthesized providing a radiation pattern as close as possible to the desired one. The problem is solved using linear integer programming procedures obtaining array designs that greatly reduce the fabrication costs. Results are provided for every method showing the capabilities that the above mentioned methods offer. The results obtained are compared with available methods in the literature. The importance of introducing a rigorous analysis into the synthesis method is emphasized and the results obtained are compared with a commercial software, showing good agreement.

Horizontal gene transfer among genomes: The complexity hypothesis

Increasingly, studies of genes and genomes are indicating that considerable horizontal transfer has occurred between prokaryotes. Extensive horizontal transfer has occurred for operational genes (those involved in housekeeping), whereas informational genes (those involved in transcription, translation, and related processes) are seldomly horizontally transferred. Through phylogenetic analysis of six complete prokaryotic genomes and the identification of 312 sets of orthologous genes present in all six genomes, we tested two theories describing the temporal flow of horizontal transfer. We show that operational genes have been horizontally transferred continuously since the divergence of the prokaryotes, rather than having been exchanged in one, or a few, massive events that occurred early in the evolution of prokaryotes. In agreement with earlier studies, we found that differences in rates of evolution between operational and informational genes are minimal, suggesting that factors other than rate of evolution are responsible for the observed differences in horizontal transfer. We propose that a major factor in the more frequent horizontal transfer of operational genes is that informational genes are typically members of large, complex systems, whereas operational genes are not, thereby making horizontal transfer of informational gene products less probable (the complexity hypothesis).

A General RNA-Binding Protein Complex That Includes the Cytoskeleton-associated Protein MAP 1A

Association of mRNA with the cytoskeleton represents a fundamental aspect of RNA physiology likely involved in mRNA transport, anchoring, translation, and turnover. We report the initial characterization of a protein complex that binds RNA in a sequence-independent but size-dependent manner in vitro. The complex includes a ∼160-kDa protein that is bound directly to mRNA and that appears to be either identical or highly related to a ∼1600-kDa protein that binds directly to mRNA in vivo. In addition, the microtubule-associated protein, MAP 1A, a cytoskeletal associated protein is a component of this complex. We suggest that the general attachment of mRNA to the cytoskeleton may be mediated, in part, through the formation of this ribonucleoprotein complex.