ISSN:0265-9247    

DOI:10.1002/bies.950160402

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

ISSN:0265-9247    

DOI:10.1002/bies.950160403

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe process of protein folding in the cell is now known to depend on the action of other proteins. These proteins include molecular chaperones, Which interact non‐covalently with proteins as they fold and improve the final yields of active protein in the cell. The precise mechanism by which molecular chaperones act is obscure. Experiments reported recently(1)show that for one molecular chaperone (Cpn60, typified by theE. coliprotein GroEL), the folding reaction is driven by cycles of binding and release of the co‐chaperone Cpn10 (known as GroES inE. coli). These alternate with binding and release of the unfolded protein substrate. These cycles come about because of the opposite effects of Cpn10 and unfolded protein on the Cpn60 complex: the former stabilises the ADP‐bound state of Cpn60, whereas the latter stimulates ADP‐ATP exchange. This model proposes that the substrate protein goes through multiple cycles of binding and release, and is released into the cavity of the Cpn60 complex where it can undergo folding without interacting with other nearby folding intermediates. This is consistent with the ability of Cpn60 proteins to enhance folding by blocking pathways to aggr

ISSN:0265-9247    

DOI:10.1002/bies.950160404

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

ISSN:0265-9247    

DOI:10.1002/bies.950160405

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractTheDrosophilacompound eye is an excellent experimental system for analysing fate induction of identifiable single cells. Each ommatidium, a unit eye, contains eight photoreceptors (R1‐R8), and the differentiation of these photoreceptors occurs in the larval eye imaginal disc in discrete steps: first R8 is determined, then R2/R5, R3/R4, R1/R6 and finally R7. Induction of R7, in particular, has been extensively studied at the molecular level. The R8 photoreceptor presents on its surface a ligand, Bride of Sevenless, that binds and activates Sevenless receptor tyrosine kinase in the R7 precursor. Autophosphorylated Sevenless initiates a Ras1‐mediated cascade, which eventually activates transcription factors in the nucleus via Raf1 and MAP kinases, resulting in R7 development. However, recent studies indicate that Sevenless (Sev) functions just to neuralize the cell and has no role in R7 fate determinationper se.It appears that the R7 fate may represent the lowest rung of a ‘neuronal ground state’, which is attained without any specific inductive cue. It is plausible that the R7 precursor is actively prevented from taking on the neuronal fate and this inhibition is removed by activation

ISSN:0265-9247    

DOI:10.1002/bies.950160406

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe Y‐box proteins are the most evolutionarily conserved nucleic acid binding proteins yet defined in bacteria, plants and animals. The central nucleic acid binding domain of the vertebrate proteins is 43% identical to a 70‐amino‐acid‐long protein (CS7.4) fromE. coli.The structure of this domain consists of an antiparallel fivestranded β‐barrel that recognizes both DNA and RNA. The diverse biological roles of these Y‐box proteins range from the control of theE. colicold‐shock stress response to the translational masking of messenger RNA in vertebrate gametes. This review discusses the organization of the prokaryotic and eukaryotic Y‐box proteins, how they interact with nucleic acids, and their biological roles, both prov

ISSN:0265-9247    

DOI:10.1002/bies.950160407

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe RAD6 pathway of budding yeast,Saccharomyces cerevisiae, is responsible for a substantial fraction of this organism's resistance to DNA damage, and also for induced mutagenesis. The pathway appears to incorporate two different recovery processes, both regulated byRAD6.The error‐prone recovery prcess accounts for only a small amount ofRAD6‐dependent resistance, but probably all induced mutagenesis. The underlying mechanism, for error‐prone recovery is very likely to be translesion synthesis. The error‐free recovery process accounts for most ofRAD6‐dependent resistace, but its mechanism is less clear; it may entail error‐free bypass by template switching and/or DNA gap filling by recombination.RAD6regulates these activities by ubiquitinateins, and the roles they play in error‐free and error‐prone recovery, have not yet b

ISSN:0265-9247    

DOI:10.1002/bies.950160408

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractAlthough the generation of reactive oxygen species is an activity normally associated with phagocytic leucocytes, mammalian spermatozoa were, in fact, the first cell type in which this activity was described. In recent years it has become apparent that spermatozoa are not the only nonphagocytic cells to exhibit a capacity for reactive oxygen species production, because this activity has been detected in a wide variety of different cells including fibroblasts, mesangial cells, oocytes, Leyding cells endothelial cells, thryroid cells, adipocytes, tumour cell and platelets. Since the capacity to generate reactive oxygen species is apparently so widespread, the risk‐benefit equation for these potentially pernicious molecules becomes a matter of intese interest. In the case of human spermatozoa, the risk of manufacturing reactive oxygen metabolites is considerable because these cells are particularly vulnerable to lipid peroxidation. Indeed, there is now good evidence to indicate that oxygen radicals are involved in the initiation of peroxidative damage to the sperm plasma membrane, seen in many cases of male infertility. This risk is off‐set by recent data suggesting that superoxide anions and hydrogen peroxide also participate in the induction of key biological events such as hyperactiavated motility and the acrosome reaction. Thus, human spermatozoa appear to use reactive oxygen species for a physiological purpose and have the difficult task of ensuring the balanced generation of these potentially harmful, but biologically important, modulators of cellular funct

ISSN:0265-9247    

DOI:10.1002/bies.950160409

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractA combination of cytogenetic and molecular analyses has shown that several different transposable elements are involved in the restructuring ofDrosophilachromosomes. Two kinds of elements,Pandhobo, are especially prone to induce chromosome rearrangements. The mechanistic details of this process are unclear, but, at least some of the time, it seems to involve ectopic recombination between elements inserted at different chromosomal sites; the available data suggest that these ectopic recombination events are much more likely to occure between elements in the same chromosome than between elements in different chromosomes. OtherDrosophilatransposons also appear to mediate chromosome restructuring by ectopic recombination; these include the retrotransposons BEL, roo, DocandIand the foldback elementFB.In addition, two retrotransposons,HeT‐AandTART, have been found to be associated specifically with the ends ofDrosophilachromosomes. Very limited data indicate that transposon‐mediated chromosome restructuring is occurring in natural populations ofDrosophila.This suggests that transposable elements may help to shape the structure of theDrosophilagenome and implies that they may have a similar role in other organi

ISSN:0265-9247    

DOI:10.1002/bies.950160410

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractTrinucleotide repeat expansions are now a well‐established mutational mechanism in human genetic disease. An unstable CAG repeat is known to be responsible for three neurodegenerative disorders: Huntington's disease, spinal and bulbar musclar atrophy and spinocerebellar ataxia type 1. Similarities in the genetics of these diseases, the size of the repeat expansions and the position of the unstable repeat within the gene (when known) suggest a common basis to the observed phenotypes. The cloning of two regions at which chromosome breakage can be induced (FRAXA and FRAXE) has in each case uncovered an unstable CG‐rich triplet repeat which becomes methylated when fully expanded. In addition to these two classes of mutation, the presence of an expanded CTG repeat in the 3′ untranslated region of a protein kinase causes myotonic dystrophy. The size of the respective expansions, repeat stability, mutational origins and possible mechanisms of action are disc

ISSN:0265-9247    

DOI:10.1002/bies.950160411

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY