What electrical measurements can say about changes in fault systems.

Earthquake zones in the upper crust are usually more conductive than the surrounding rocks, and electrical geophysical measurements can be used to map these zones. Magnetotelluric (MT) measurements across fault zones that are parallel to the coast and not too far away can also give some important information about the lower crustal zone. This is because the long-period electric currents coming from the ocean gradually leak into the mantle, but the lower crust is usually very resistive and very little leakage takes place. If a lower crustal zone is less resistive it will be a leakage zone, and this can be seen because the MT phase will change as the ocean currents leave the upper crust. The San Andreas Fault is parallel to the ocean boundary and close enough to have a lot of extra ocean currents crossing the zone. The Loma Prieta zone, after the earthquake, showed a lot of ocean electric current leakage, suggesting that the lower crust under the fault zone was much more conductive than normal. It is hard to believe that water, which is responsible for the conductivity, had time to get into the lower crustal zone, so it was probably always there, but not well connected. If this is true, then the poorly connected water would be at a pressure close to the rock pressure, and it may play a role in modifying the fluid pressure in the upper crust fault zone. We also have telluric measurements across the San Andreas Fault near Palmdale from 1979 to 1990, and beginning in 1985 we saw changes in the telluric signals on the fault zone and east of the fault zone compared with the signals west of the fault zone. These measurements were probably seeing a better connection of the lower crust fluids taking place, and this may result in a fluid flow from the lower crust to the upper crust. This could be a factor in changing the strength of the upper crust fault zone.

A complexity measure for selective matching of signals by the brain.

We have previously derived a theoretical measure of neural complexity (CN) in an attempt to characterize functional connectivity in the brain. CN measures the amount and heterogeneity of statistical correlations within a neural system in terms of the mutual information between subsets of its units. CN was initially used to characterize the functional connectivity of a neural system isolated from the environment. In the present paper, we introduce a related statistical measure, matching complexity (CM), which reflects the change in CN that occurs after a neural system receives signals from the environment. CM measures how well the ensemble of intrinsic correlations within a neural system fits the statistical structure of the sensory input. We show that CM is low when the intrinsic connectivity of a simulated cortical area is randomly organized. Conversely, CM is high when the intrinsic connectivity is modified so as to differentially amplify those intrinsic correlations that happen to be enhanced by sensory input. When the input is represented by an individual stimulus, a positive value of CM indicates that the limited mutual information between sensory sheets sampling the stimulus and the rest of the brain triggers a large increase in the mutual information between many functionally specialized subsets within the brain. In this way, a complex brain can deal with context and go "beyond the information given."

Nuclear localization signals of human and Thermoplasma proteasomal alpha subunits are functional in vitro.

Proteasomes are located both in the nuclei and in the cytoplasm of eukaryotic cells. Active transport of these complexes through the nuclear pores has been proposed to be mediated by nuclear localization signals (NLS), which have been found in several of the alpha-type proteasomal subunits. We have tested three different putative NLS sequences from human alpha-type proteasomal subunits (Hsc iota, Hsc9, and Hsc3), as well as a putative NLS-type sequence from the archaeon Thermoplasma acidophilum, for their ability to direct non-nuclear proteins to the nucleus. Synthetic peptides containing these putative NLS sequences were generated and conjugated to large fluorescent reporter molecules: allophycocyanin or fluorescein-labeled bovine serum albumin. The conjugates were introduced into digitonin-permeabilized HeLa and 3T3 cells in the presence of cell lysate and ATP, and nuclear import was monitored by fluorescence microscopy. All three putative NLS sequences from human proteasomal subunits were able to direct the reporter molecules to the nucleus in both cell types, although differences in efficiency were observed. Substitution of threonine for the first lysine residue of the eukaryotic NLS motifs inhibited nuclear import completely. Interestingly, the putative NLS sequence found in T. acidophilum was also functional as a nuclear targeting sequence.

Identification of signals required for the insertion of heterologous genome segments into the reovirus genome.

In cells simultaneously infected with any two of the three reovirus serotypes ST1, ST2, and ST3, up to 15% of the yields are intertypic reassortants that contain all possible combinations of parental genome segments. We have now found that not all genome segments in reassortants are wild type. In reassortants that possess more ST1 than ST3 genome segments, all ST1 genome segments appear to be wild type, but the incoming ST3 genome segments possess mutations that make them more similar to the ST1 genome segments that they replace. In reassortants resulting from crosses of the more distantly related ST3 and ST2 viruses that possess a majority of ST3 genome segments, all incoming ST2 genome segments are wild type, but the ST3 S4 genome segment possesses two mutations, G74 to A and G624 to A, that function as acceptance signals. Recognition of these signals has far-reaching implications for the construction of reoviruses with novel properties and functions.

Processing of speech signals for physical and sensory disabilities.

Assistive technology involving voice communication is used primarily by people who are deaf, hard of hearing, or who have speech and/or language disabilities. It is also used to a lesser extent by people with visual or motor disabilities. A very wide range of devices has been developed for people with hearing loss. These devices can be categorized not only by the modality of stimulation [i.e., auditory, visual, tactile, or direct electrical stimulation of the auditory nerve (auditory-neural)] but also in terms of the degree of speech processing that is used. At least four such categories can be distinguished: assistive devices (a) that are not designed specifically for speech, (b) that take the average characteristics of speech into account, (c) that process articulatory or phonetic characteristics of speech, and (d) that embody some degree of automatic speech recognition. Assistive devices for people with speech and/or language disabilities typically involve some form of speech synthesis or symbol generation for severe forms of language disability. Speech synthesis is also used in text-to-speech systems for sightless persons. Other applications of assistive technology involving voice communication include voice control of wheelchairs and other devices for people with mobility disabilities.

Interleukin 4 signals through two related pathways.

The interleukin 4 (IL-4) signaling pathway involves activation, by tyrosine phosphorylation, of two distinct substrates, a signal-transducing factor (STF-IL4) and the IL-4-induced phosphotyrosine substrate (4PS). It is not known whether the IL-4-mediated activation of these substrates occurs via related or distinct signaling pathways. We report that 32D cells, an IL-3-dependent myeloid progenitor cell line in which no phosphorylated 4PS is found, activate high levels of STF-IL4 in response to IL-4. Consistent with the known requirement for 4PS or insulin receptor substrate 1 (IRS-1) in IL-4-mediated mitogenesis, activation of STF-IL4 in 32D cells is not sufficient for IL-4-inducible c-myc expression. In addition, we have examined the ability of 32D cells transfected with different truncation mutants of the human IL-4 receptor to activate Jak-3 kinase and STF-IL4 in response to human IL-4. As in the case of 4PS/IRS-1, we have found that activation of both Jak-3 and STF-IL4 requires the presence of the IL-4 receptor region comprising aa 437-557. The finding that the same region of the IL-4 receptor is required for the induction of both 4PS/IRS-1 and STF-IL4 suggests that the IL-4-stimulated activation of these two substrates might involve common factors.

Protein secretion by enteropathogenic Escherichia coli is essential for transducing signals to epithelial cells.

Enteropathogenic Escherichia coli (EPEC), a major cause of pediatric diarrhea, adheres to epithelial cells and activates host cell signal transduction pathways. We have identified five proteins that are secreted by EPEC and show that this secretion process is critical for triggering signal transduction events in epithelial cells. Protein secretion occurs via two pathways: one secretes a 110-kDa protein and the other mediates export of the four remaining proteins. Secretion of all five proteins was regulated by temperature and the perA locus, two factors which regulate expression of other known EPEC virulence factors. Amino-terminal sequence analysis of the secreted polypeptides identified one protein (37 kDa) as the product of the eaeB gene, a genetic locus previously shown to be necessary for signal transduction. A second protein (39 kDa) showed significant homology with glyceraldehyde-3-phosphate dehydrogenase, while the other three proteins (110, 40, and 25 kDa) were unique. The secreted proteins associated with epithelial cells, and EaeB became resistant to protease digestion upon association, suggesting that intimate interactions are required for transducing signals.

Interferon gamma signals via a high-affinity multisubunit receptor complex that contains two types of polypeptide chain.

Signaling by interferon gamma (IFN-gamma) requires two structurally related cell surface proteins: a ligand-binding polypeptide, known as the IFN-gamma receptor (IFN-gamma R), and an accessory factor. However, it is not known whether IFN-gamma forms a ternary complex with the IFN-gamma R and accessory factor to initiate signaling. Here we demonstrate complex formation between IFN-gamma and the two proteins, both in solution and at the cell surface. We observe complexes containing ligand, two molecules of IFN-gamma R (designated the IFN-gamma R alpha chain), and one or two molecules of accessory factor (designated the IFN-gamma R beta chain). Transfected cells expressing both IFN-gamma R chains bind IFN-gamma with higher affinity than do cells expressing alpha chain alone. Anti-beta-chain antibodies prevent the beta chain from participating in the ligand-receptor complex, reduce the affinity for IFN-gamma, and block signaling. Soluble alpha- or beta-chain extracellular domains also inhibit function. These results demonstrate that IFN-gamma signals via a high-affinity multisubunit complex that contains two types of receptor chain and suggest a potential approach to inhibiting specific actions of IFN-gamma by blocking the association of receptor subunits.

Phosphatidylinositol 3-kinase signals activation of p70 S6 kinase in situ through site-specific p70 phosphorylation.

The p70 S6 kinase is activated by insulin and mitogens through multisite phosphorylation of the enzyme. One set of activating phosphorylations occurs in a putative autoinhibitory domain in the noncatalytic carboxyl-terminal tail. Deletion of this tail yields a variant (p70 delta CT104) that nevertheless continues to be mitogen regulated. Coexpression with a recombinant constitutively active phosphatidylinositol (PI) 3-kinase (EC 2.7.1.137) gives substantial activation of both full-length p70 and p70 delta CT104 but not Rsk. Activation of p70 delta CT104 by PI 3-kinase and inhibition by wortmannin are each accompanied by parallel and selective changes in the phosphorylation of p70 Thr-252. A Thr or Ser at this site, in subdomain VIII of the catalytic domain just amino-terminal to the APE motif, is necessary for p70 40S kinase activity. The inactive ATP-binding site mutant K123M p70 delta CT104 undergoes phosphorylation of Thr-252 in situ but does not undergo direct phosphorylation by the active PI 3-kinase in vitro. PI 3-kinase provides a signal necessary for the mitogen activation of the p70 S6 kinase, which directs the site-specific phosphorylation of Thr-252 in the p70 catalytic domain, through a distinctive signal transduction pathway.

Signals involved in wound-induced proteinase inhibitor II gene expression in tomato and potato plants.

Chemical and physical signals have been reported to mediate wound-induced proteinase inhibitor II (Pin2) gene expression in tomato and potato plants. Among the chemical signals, phytohormones such as abscisic acid (ABA) and jasmonic acid (JA) and the peptide systemin represent the best characterized systems. Furthermore, electrical and hydraulic mechanisms have also been postulated as putative Pin2-inducing systemic signals. Most of the chemical agents are able to induce Pin2 gene expression without any mechanical wounding. Thus, ABA, JA, and systemin initiate Pin2 mRNA accumulation in the directly treated leaves and in the nontreated leaves (systemic) that are located distal to the treated ones. ABA-deficient tomato and potato plants do not respond to wounding by accumulation of Pin2 mRNA, therefore providing a suitable model system for analysis of the signal transduction pathway involved in wound-induced gene activation. It was demonstrated that the site of action of JA is located downstream to the site of action of ABA. Moreover, systemin represents one of the initial steps in the signal transduction pathway regulating the wound response. Recently, it was reported that heat treatment and mechanical injury generate electrical signals, which propagate throughout the plant. These signals are capable of inducing Pin2 gene expression in the nontreated leaves of wounded plants. Furthermore, electrical current application to tomato leaves leads to an accumulation of Pin2 mRNA in local and systemic tissues. Examination of photosynthetic parameters (assimilation and transpiration rate) on several types of stimuli suggests that heat-induced Pin2 gene expression is regulated by an alternative pathway from that mediating the electrical current and mechanical wound response.

Oligogalacturonide defense signals in plants: large fragments interact with the plasma membrane in vitro.

Oligogalacturonides are plant cell wall-derived regulatory molecules which stimulate defense gene expression during pathogenesis. In vitro, these compounds enhance the phosphorylation of an approximately 34-kDa protein (pp34) in purified plasma membranes from potato and tomato leaves. We now show that polygalacturonate-enhanced phosphorylation of pp34 occurs in plasma membranes purified from tomato roots, hypocotyls, and stems and from undifferentiated potato cells. Furthermore, a similar phosphorylation is detected in leaf plasma membranes from soybean, a plant distantly related to tomato. Purified oligogalacturonides 13 to at least 26 residues long stimulate pp34 thiophosphorylation in vitro. This stimulation pattern differs from the induction of many known defense responses in vivo, where a narrower range of smaller fragments, between approximately 10 and 15 residues long, are active. On the basis of these differences we suggest that observed effects of applied exogenous oligogalacturonides on defense responses may not necessarily reflect the situation during pathogenesis. The cell wall could act as a barrier to many exogenous oligo- and polygalacturonides as well as other large regulatory ligands.

Redundant 3' end-forming signals for the yeast CYC1 mRNA.

The cyc1-512 mutation is a 38-bp deletion in the 3' untranslated region of the CYC1 gene, which encodes iso-1-cytochrome c in Saccharomyces cerevisiae. This deletion caused a 90% reduction in the levels of the CYC1 mRNA and protein because of the absence of the normal 3' end-forming signal. Although the 3' end-forming signal was not defined by previous analyses, we report that concomitant alteration by base-pair substitution of three 3' end-forming signals within and adjacent to the 38-bp region produced the same phenotype as the cyc1-512 mutation. Furthermore, these signals appear to be related to the previously identified 3' end-forming signal TATATA. A computer analysis revealed that TATATA and related sequences were present in the majority of 3' untranslated regions of yeast genes. Although TATATA may be the strongest and most frequently used signal in yeast genes, the CYC1+ gene concomitantly employed the weaker signals TT-TATA, TATGTT, and TATTTA, resulting in a strong signal.

Two nuclear localization signals present in the basic-helix 1 domains of MyoD promote its active nuclear translocation and can function independently.

MyoD, a member of the family of helix-loop-helix myogenic factors that plays a crucial role in skeletal muscle differentiation, is a nuclear phosphoprotein. Using microinjection of purified MyoD protein into rat fibroblasts, we show that the nuclear import of MyoD is a rapid and active process, being ATP and temperature dependent. Two nuclear localization signals (NLSs), one present in the basic region and the other in the helix 1 domain of MyoD protein, are demonstrated to be functional in promoting the active nuclear transport of MyoD. Synthetic peptides spanning these two NLSs and biochemically coupled to IgGs can promote the nuclear import of microinjected IgG conjugates in muscle and nonmuscle cells. Deletion analysis reveals that each sequence can function independently within the MyoD protein since concomittant deletion of both sequences is required to alter the nuclear import of this myogenic factor. In addition, the complete cytoplasmic retention of a beta-galactosidase-MyoD fusion mutant protein, double deleted at these two NLSs, argues against the existence of another functional NLS motif in MyoD.

Residue replacements of buried aspartyl and related residues in sensory rhodopsin I: D201N produces inverted phototaxis signals.

Residue replacements were made at five positions (Arg-73, Asp-76, Tyr-87, Asp-106, and Asp-201) in the Halobacterium salinarium phototaxis receptor sensory rhodopsin I (SR-I) by site-specific mutagenesis. The sites were chosen for their correspondence in position to residues of functional importance in the homologous light-driven proton pump bacteriorhodopsin found in the same organism. This work identifies a residue in SR-I shown to be of vital importance to its attractant signaling function: Asp-201. The effect of the substitution with the isosteric asparagine is to convert the normally attractant signal of orange light stimulation to a repellent signal. In contrast, similar neutral substitution of the four other ionizable residues near the photoactive site allows essentially normal attractant and repellent phototaxis signaling. Wild-type two-photon repellent signaling by the receptor is intact in the Asp-201 mutant, genetically separating the wild-type attractant and repellent signal generation processes. A possible explanation and implications of the inverted signaling are discussed. Results of neutral residue substitution for Asp-76 confirm our previous evidence that proton transfer reactions involving this residue are not important to phototaxis but that Asp-76 functions as the Schiff base proton acceptor in proton translocation by transducer-free SR-I.

Control of somite patterning by signals from the lateral plate.

The body musculature of higher vertebrates is composed of the epaxial muscles, associated with the vertebral column, and of the hypaxial muscles of the limbs and ventro-lateral body wall. Both sets of muscles arise from different cell populations within the dermomyotomal component of the somite. Myogenesis first occurs in the medial somitic cells that will form the epaxial muscles and starts with a significant delay in cells derived from the lateral somitic moiety that migrate to yield the hypaxial muscles. The newly formed somite is mostly composed of unspecified cells, and the determination of somitic compartments toward specific lineages is controlled by environmental cues. In this report, we show that determinant signals for lateral somite specification are provided by the lateral plate. They result in a blockade of the myogenic program, which maintains the lateral somitic cells as undifferentiated muscle progenitors expressing the Pax-3 gene, and represses the activation of the MyoD family genes. In vivo, this mechanism could account for the delay observed in the onset of myogenesis between muscles of the epaxial and hypaxial domains.