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361.
Partition of tRNA synthetases into two classes based on mutually exclusive sets of sequence motifs 总被引:108,自引:0,他引:108
The aminoacyl-transfer RNA synthetases (aaRS) catalyse the attachment of an amino acid to its cognate transfer RNA molecule in a highly specific two-step reaction. These proteins differ widely in size and oligomeric state, and have limited sequence homology. Out of the 18 known aaRS, only 9 referred to as class I synthetases (GlnRS, TyrRS, MetRS, GluRS, ArgRS, ValRS, IleRS, LeuRS, TrpRS), display two short common consensus sequences ('HIGH' and 'KMSKS') which indicate, as observed in three crystal structures, the presence of a structural domain (the Rossman fold) that binds ATP. We report here the sequence of Escherichia coli ProRS, a dimer of relative molecular mass 127,402, which is homologous to both ThrRS and SerRS. These three latter aaRS share three new sequence motifs with AspRS, AsnRS, LysRS, HisRS and the beta subunit of PheRS. These three motifs (motifs 1, 2 and 3), in a search through the entire data bank, proved to be specific for this set of aaRS (referred to as class II). Class II may also contain AlaRS and GlyRS, because these sequences have a typical motif 3. Surprisingly, this partition of aaRS in two classes is found to be strongly correlated on the functional level with the acylation occurring either on the 2' OH (class I) or 3' OH (class II) of the ribose of the last nucleotide of tRNA. 相似文献
362.
Bcl-2 is an inner mitochondrial membrane protein that blocks programmed cell death 总被引:174,自引:0,他引:174
The t(14; 18) chromosomal translocation of human follicular B-cell lymphoma juxtaposes the bcl-2 gene with the immunoglobulin heavy chain locus. The bcl-2 immunoglobulin fusion gene is markedly deregulated resulting in inappropriately elevated levels of bcl-2 RNA and protein. Transgenic mice bearing a bcl-2 immunoglobulin minigene demonstrate a polyclonal expansion of resting yet responsive IgM-IgD B cells which display prolonged cell survival but no increase in cell cycling. Moreover, deregulated bcl-2 extends the survival of certain haematopoietic cell lines following growth-factor deprivation. By using immunolocalization studies we now demonstrate that Bcl-2 is an integral inner mitochondrial membrane protein of relative molecular mass 25,000 (25k). Overexpression of Bcl-2 blocks the apoptotic death of a pro-B-lymphocyte cell line. Thus, Bcl-2 is unique among proto-oncogenes, being localized to mitochondria and interfering with programmed cell death independent of promoting cell division. 相似文献
363.
Phospholipid binding by a synaptic vesicle protein homologous to the regulatory region of protein kinase C 总被引:43,自引:0,他引:43
Neurotransmitters are released at synapses by the Ca2(+)-regulated exocytosis of synaptic vesicles, which are specialized secretory organelles that store high concentrations of neurotransmitters. The rapid Ca2(+)-triggered fusion of synaptic vesicles is presumably mediated by specific proteins that must interact with Ca2+ and the phospholipid bilayer. We now report that the cytoplasmic domain of p65, a synaptic vesicle-specific protein that binds calmodulin contains an internally repeated sequence that is homologous to the regulatory C2-region of protein kinase C (PKC). The cytoplasmic domain of recombinant p65 binds acidic phospholipids with a specificity indicating an interaction of p65 with the hydrophobic core as well as the headgroups of the phospholipids. The binding specificity resembles PKC, except that p65 also binds calmodulin, placing the C2-regions in a context of potential Ca2(+)-regulation that is different from PKC. This is a novel homology between a cellular protein and the regulatory domain of protein kinase C. The structure and properties of p65 suggest that it may have a role in mediating membrane interactions during synaptic vesicle exocytosis. 相似文献
364.
More false-positive problems 总被引:9,自引:0,他引:9
365.
Stimulus-secretion coupling in exocrine glands involves Ca2+ release from intracellular stores. In endoplasmic reticulum vesicle preparations from rat exocrine pancreas, an inositol 1,4,5-trisphosphate(InsP3)-sensitive, as well as an InsP3-insensitive, Ca2+ pool has been characterized. But Ca2+ channels in the endoplasmic reticulum of rat exocrine pancreas have not been demonstrated at the level of single-channel current. We have now used the patch-clamp technique on endoplasmic reticulum vesicles fused by means of the dehydration-rehydration method. In excised patches, single Ba2(+)- and Ca2(+)-selective channels were recorded. The channel activity was markedly voltage-dependent. Caffeine increased channel open-state probability, whereas ruthenium red and Cd2+ blocked single-channel currents. Ryanodine, nifedipine and heparin had no effect on channel activity. The channel activity was not dependent on the free Ca2+ concentration, the presence of InsP3, or pH. We conclude that this calcium channel mediates Ca2+ release from an intracellular store through an InsP3-insensitive mechanism. 相似文献
366.
367.
N M Gough D P Gearing N A Nicola E Baker M Pritchard D F Callen G R Sutherland 《Nature》1990,345(6277):734-736
Mammalian sex chromosomes share a small terminal region of homologous DNA sequences, which pair and recombine during male meiosis. Alleles in this region can be exchanged between X and Y chromosomes and are therefore inherited as if autosomal. Genes from this so-called pseudoautosomal region (PAR) are present in two doses in both males and females, and escape inactivation of the X chromosome in females. Indirect evidence suggests that there must be several pseudoautosomal genes, and several candidates have been proposed. Until now, the only gene that has been unequivocally located in the PAR is MIC2, which encodes a cell-surface antigen of unknown function. We now report the localization of a gene of known function to this region--the gene for the receptor of the haemopoietic regulator, granulocyte-macrophage colony stimulating factor. The chromosomal localization of this gene may be important in understanding the generation of M2 acute myeloid leukaemia. 相似文献
368.
本文阐述了水轮机变结构变参数调速控制的基本问题,提出了相应的控制策略,并论证该控制策略的稳定性、最优性。仿真结果表明本文提出的策略控制效果优良。 相似文献
369.
本文提出了智能化自完善控制策略,通过采用“知识库”存贮最佳的知识与经验,根据受控对象当前运行条件及状态,运用相应的分析逻辑及推理功能,实时地调整控制器结构及参数,以实现逐步改善控制系统性能的目的.文中将所论述的控制策略用于水轮机调速器开发研究. 相似文献
370.