Isolation, regulation, and DNA-binding properties of three Drosophila nuclear hormone receptor superfamily members.

We have designed a rapid cloning and screening strategy to identify new members of the nuclear hormone receptor superfamily that are expressed during the onset of Drosophila metamorphosis. Using this approach, we isolated three Drosophila genes, designated DHR38, DHR78, and DHR96. All three genes are expressed throughout third-instar larval and prepupal development. DHR38 is the Drosophila homolog of NGFI-B and binds specifically to an NGFI-B response element. DHR78 and DHR96 are orphan receptor genes. DHR78 is induced by 20-hydroxyecdysone (20E) in cultured larval organs, and its encoded protein binds to two AGGTCA half-sites arranged as either direct or palindromic repeats. DHR96 is also 20E-inducible, and its encoded protein binds selectively to the hsp27 20E response element. The 20E receptor can bind to each of the sequences recognized by DHR78 and DHR96, indicating that these proteins may compete with the receptor for binding to a common set of target sequences.

Plant members of a family of sulfate transporters reveal functional subtypes.

Three plant sulfate transporter cDNAs have been isolated by complementation of a yeast mutant with a cDNA library derived from the tropical forage legume Stylosanthes hamata. Two of these cDNAs, shst1 and shst2, encode high-affinity H+/sulfate cotransporters that mediate the uptake of sulfate by plant roots from low concentrations of sulfate in the soil solution. The third, shst3, represents a different subtype encoding a lower affinity H+/sulfate cotransporter, which may be involved in the internal transport of sulfate between cellular or subcellular compartments within the plant. The steady-state level of mRNA corresponding to both subtypes is subject to regulation by signals that ultimately respond to the external sulfate supply. These cDNAs represent the identification of plant members of a family of related sulfate transporter proteins whose sequences exhibit significant amino acid conservation in filamentous fungi, yeast, plants, and mammals.

Simian virus 40 late gene expression is regulated by members of the steroid/thyroid hormone receptor superfamily.

Transcription of the late genes of simian virus 40 (SV40) is repressed during the early phase of the lytic cycle of infection of binding of cellular factors, called IBP-s, to the SV40 late promoter; repression is relieved after the onset of viral DNA replication by titration of these repressors. Preliminary data indicated that one of the major components of IBP-s was human estrogen-related receptor 1 (hERR1). We show here that several members of the steroid/thyroid hormone receptor superfamily, including testis receptor 2, thyroid receptor alpha 1 in combination with retinoid X receptor alpha, chicken ovalbumin upstream promoter transcription factors 1 and 2 (COUP-TF1 and COUP-TF2), as well as hERR1, possess the properties of IBP-s. These receptors bind specifically to hormone receptor binding sites present in the SV40 major late promoter. Recombinant COUP-TF1 specifically represses transcription from the SV40 major late promoter in a cell-free transcription system. Expression of COUP-TF1, COUP-TF2, or hERR1 in monkey cells results in repression of the SV40 late promoter, but not the early promoter, in the absence of the virally encoded large tumor antigen. Overexpression of COUP-TF1 leads to a delay in the early-to-late switch in SV40 gene expression during the lytic cycle of infection. Thus, members of this superfamily can play major direct roles in regulating expression of SV40. Possibly, natural or synthetic ligands to these receptors can serve as antiviral drugs. Our findings also provide the basis for the development of assays to screen for the ligands to testis receptor 2 and hERR1.

Multiple Bcl-2 family members demonstrate selective dimerizations with Bax.

A family of Bcl-2-related proteins regulates cell death and shares highly conserved BH1 and BH2 domains. BH1 and BH2 domains of Bcl-2 were required for it to heterodimerize with Bax and to repress apoptosis. A yeast two-hybrid assay accurately reproduced this interaction and defined a selectivity and hierarchy of further dimerizations. Bax also heterodimerizes with Bcl-xL, Mcl-1, and A1. A Gly-159-->Ala substitution in BH1 of Bcl-xL disrupted its heterodimerization with Bax and abrogated its inhibition of apoptosis in mammalian cells. This suggests that the susceptibility to apoptosis is determined by multiple competing dimerizations in which Bax may be a common partner.

Functional interactions between the retinoblastoma (Rb) protein and Sp-family members: superactivation by Rb requires amino acids necessary for growth suppression.

The transient expression of the retinoblastoma protein (Rb) regulates the transcription of a variety of growth-control genes, including c-fos, c-myc, and the gene for transforming growth factor beta 1 via discrete promoter sequences termed retinoblastoma control elements (RCE). Previous analyses have shown that Sp1 is one of three RCE-binding proteins identified in nuclear extracts and that Rb functionally interacts with Sp1 in vivo, resulting in the "superactivation" of Sp1-mediated transcription. By immunochemical and biochemical criteria, we report that an Sp1-related transcription factor, Sp3, is a second RCE-binding protein. Furthermore, in transient cotransfection assays, we report that Rb "superactivates" Sp3-mediated RCE-dependent transcription in vivo and that levels of superactivation are dependent on the trans-activator (Sp1 or Sp3) studied. Using expression vectors carrying mutated Rb cDNAs, we have identified two portions of Rb required for superactivation: (i) a portion of the Rb "pocket" (amino acids 614-839) previously determined to be required for physical interactions between Rb and transcription factors such as E2F-1 and (ii) a novel amino-terminal region (amino acids 140-202). Since both of these regions of Rb are targets of mutation in human tumors, our data suggest that superactivation of Sp1/Sp3 may play a role in Rb-mediated growth suppression and/or the induction of differentiation.

Fadiga cíclica flexural de instrumentos Hyflex CM e TF Adaptive em diferentes situações experimentais

O presente estudo teve como objetivo avaliar a resistência à fadiga cíclica flexural dos instrumentos de níquel- titânio, Hyflex CM (Coltène, EUA) e TF Adaptive (SybronEndo, EUA) em diferentes situações experimentais. Todas as limas que foram selecionadas possuíam conicidade 0,04 e diâmetro de ponta 35. Utilizou-se um dispositivo desenvolvido especificamente para realizar o ensaio flexural dinâmico. Os instrumentos TF Adaptive foram divididos em 3 grupos de acordo com o ângulo de curvatura do ensaio: 45º, 60º e 90º e cada grupo subdividido em 2 subgrupos de acordo com o tipo de movimento: rotação contínua e Adaptive. Cada subgrupo era composto por 15 instrumentos TF Adaptive, totalizando 90 instrumentos. Quinze instrumentos Hyflex CM formavam o grupo 4, no ensaio com ângulo de curvatura 90 graus e rotação contínua. A simulação foi realizada em canais artificiais de aço com ângulo de 45, 60, 90 graus e raio 5m m. O número de ciclos e o tempo em segundos até a fratura foram tabulados e analisados. Entretanto, a fadiga cíclica flexural foi significante maior nos três grupos em movimento Adaptive. E as limas TF Adaptive em seu próprio movimento tiveram maior número de ciclos e tempo até a fratura quando comparadas as Hyflex CM no ensaio de 90 graus. Portanto, conclui-se que o sistema Adaptive (limas TF Adaptive + movimento Adaptive) foi mais seguro à resistência á fadiga flexural, e no ensaio de 90 graus o sistema Adaptive foi mais resistente quando comparado com as limas Hyflex CM no movimento de rotação contínua.

A spectroscopy study of nearby late-type stars, possible members of stellar kinematic groups

Context. Nearby late-type stars are excellent targets for seeking young objects in stellar associations and moving groups. The origin of these structures is still misunderstood, and lists of moving group members often change with time and also from author to author. Most members of these groups have been identified by means of kinematic criteria, leading to an important contamination of previous lists by old field stars. Aims. We attempt to identify unambiguous moving group members among a sample of nearby-late type stars by studying their kinematics, lithium abundance, chromospheric activity, and other age-related properties. Methods. High-resolution echelle spectra (R ~ 57 000) of a sample of nearby late-type stars are used to derive accurate radial velocities that are combined with the precise Hipparcos parallaxes and proper motions to compute galactic-spatial velocity components. Stars are classified as possible members of the classical moving groups according to their kinematics. The spectra are also used to study several age-related properties for young late-type stars, i.e., the equivalent width of the lithium Li i 6707.8 Å line or the R'_HK index. Additional information like X-ray fluxes from the ROSAT All-Sky Survey or the presence of debris discs is also taken into account. The different age estimators are compared and the moving group membership of the kinematically selected candidates are discussed. Results. From a total list of 405 nearby stars, 102 have been classified as moving group candidates according to their kinematics. i.e., only ~25.2% of the sample. The number reduces when age estimates are considered, and only 26 moving group candidates (25.5% of the 102 candidates) have ages in agreement with the star having the same age as an MG member.

Post T Tauri stars in the solar neighborhood: isolated or members of young associations and moving groups

Post T Tauri stars (PTTS) are late-type stars in the age range between 10 and 100 Myr filling the gap between T Tauri (TTs) and zero-age: main sequence phases. This period of evolution remains ambiguous and until now different studies of young stars have failed to find the numbers of PTTS that are expected. In the last years, some PTTS have been identified among the X-ray detected pre-main sequence stars in some star-forming regions. More recently, additional PTTS have been identified in young associations and moving groups (β Pic, TW Hya, Tucana/Horologium, and the AB Dor). However, many isolated PTTS still remain undiscovered. In this contribution, we compiled the PTTS previously identified in the literature, and identified new candidates using the information provided by the high resolution spectra obtained during our surveys of late-type stars possible members to young moving groups, FGK stars in the solar neighborhood, and RasTyc sample. To identify PTTS we applied an age-oriented definition using relative age indicators (Li abundance, chromospheric and coronal emission and the kinematics) as well as color-magnitude diagrams and pre-main sequence isochrones.

Efficient intrinsic spin relaxation in graphene due to flexural distortions

We propose an intrinsic spin scattering mechanism in graphene originated by the interplay of atomic spin-orbit interaction and the local curvature induced by flexural distortions of the atomic lattice. Starting from a multiorbital tight-binding Hamiltonian with spin-orbit coupling considered non-perturbatively, we derive an effective Hamiltonian for the spin scattering of the Dirac electrons due to flexural distortions. We compute the spin lifetime due to both flexural phonons and ripples and we find values in the 1-10 ns range at room temperature. The proposed mechanism dominates the spin relaxation in high mobility graphene samples and should also apply to other planar aromatic compounds.

Anisotropic intrinsic spin relaxation in graphene due to flexural distortions

We propose an intrinsic spin scattering mechanism in graphene originated by the interplay of atomic spin-orbit interaction and the local curvature induced by flexural distortions of the atomic lattice. Starting from a multiorbital tight-binding Hamiltonian with spin-orbit coupling considered nonperturbatively, we derive an effective Hamiltonian for the spin scattering of the Dirac electrons due to flexural distortions. We compute the spin lifetime due to both flexural phonons and ripples and we find values in the microsecond range at room temperature. Interestingly, this mechanism is anisotropic on two counts. First, the relaxation rate is different for off-plane and in-plane spin quantization axis. Second, the spin relaxation rate depends on the angle formed by the crystal momentum with the carbon-carbon bond. In addition, the spin lifetime is also valley dependent. The proposed mechanism sets an upper limit for spin lifetimes in graphene and will be relevant when samples of high quality can be fabricated free of extrinsic sources of spin relaxation.

Members of the General Court, 1798-1799

Notebook with paper cover containing a handwritten list of the members of the Massachusetts General Court arranged by county and town. Pearson identified characteristics of the politicians including whether they were chosen by the people or Legislature, were for or against the College, were for or against the Virginia Resolutions, and whether they were "a good Federalist."

Lists of Phi Beta Kappa's new members, 1790, 1793, and 1797

Shapleigh served as Secretary of Harvard's chapter of Phi Beta Kappa in 1797.

Letters to family members, 1799

Four letters dated March 11, 1799, written from debtors' prison ("Debtors' Apartment") in Philadelphia. Includes descriptions of his life in the prison and fellow prisoners.

List of members of the Harvard College Class of 1797, created 1794 July 2

This document lists all the members of the Harvard College Class of 1797, including those who did not graduate. The list is roughly alphabetical, and each student's home town is listed alongside his name. There are also brief notes about one member of the class's nine-month suspension and several others' "taking up connections." The creator of this list is unknown.