摘要:

AbstractSupernumerary B chromosomes are dispensable elements of the genome which can be retained in populations at high frequencies, despite being deleterious, through the ability to undergo non‐Mendelian inheritance. Their mode of origin is, however, obscure. Recent work on gynogenetic fish has demonstrated the incorporation of small, unstable, centromere‐containing microchromosomes, probably of interspecific derivation, into an asexual lineage(1). That these resemble B chromosomes both in structure and behaviour is consistent with the proposal that hybridisation between closely related species may be a significant mode of origin for such selfish genetic elements. Additional work on the B chromosome of a parasitoid wasp and observations on patterns of chromosome breakage from somatic cell hybrids also support this hypothe

ISSN:0265-9247    

DOI:10.1002/bies.950170702

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

年代:1995

数据来源: WILEY

摘要:

AbstractGenetic analysis is revealing molecular components of circadian rhythms. The gene products of theperiodgene inDrosophilaand thefrequencygene inNeurosporaoscillate with a circadian rhythm. A recent paper(1)has shown that the PERIOD protein can undergo both intermolecular and intramolecular interactionsin vitro. The effects of temperature and twoperiodmutations on these molecular interactions were compared to the effects of the mutations and temperature on thein vivoperiod length of circadian rhythms. The results suggest that the molecular interactions may compete to maintain a rhythm with a constant period over a wide temperature range.

ISSN:0265-9247    

DOI:10.1002/bies.950170703

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

年代:1995

数据来源: WILEY

摘要:

AbstractIn higher eukaryotes, ‘replication factories’ coordinate DNA synthesis within local clusters of chromatin domains. Recent experiments(1,2)have confirmed the complexity of these clusters and established that the organization of sites labelled during S phase persists throughout the cell cycle. This implies that domain clusters are critical elements of an hierarchy that is fundamental to both nuclear and chromosome struct

ISSN:0265-9247    

DOI:10.1002/bies.950170704

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

年代:1995

数据来源: WILEY

摘要:

AbstractAlzheimer's disease, a form of senile dementia, is characterised by two kinds of pathological deposits in the brain, called plaques and tangles. The molecular nature of the deposits has been identified but there is as yet little understanding of the underlying biochemistry and cell biology that lead to their formation. Progress in this area would be greatly aided by a realistic animal model. Two recent papers describe the production of transgenic mice that develop significant aspects of Alzheimer‐like pathology. The mice produced by Gameset al.(1)develop plaques while those produced by Götzet al.(2)display the early stages of tangle patholo

ISSN:0265-9247    

DOI:10.1002/bies.950170705

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

年代:1995

数据来源: WILEY

摘要:

AbstractBacteria do many things as organized populations. We have recently learned much about the molecular basis of intercellular communication among prokaryotes. Colonies display bacterial capacities for multicellular coordination which can be useful in nature where bacteria predominantly grow as films, chains, mats and colonies.E. colicolonies are organized into differentiated non‐clonal populations and undergo complex morphogenesis. Multicellularity regulates many aspects of bacterial physiology, including DNA rearrangement systems. In some bacterial species, colony development involves swarming (active migration of cell groups). Swarm colony development displays precise geometrical controls and periodic phenomena. MotileE. colicells in semi‐solid media form organized patterns due to chemotactic autoaggregation. On poor media,B. subtilisforms branched colonies using group motility and longrange chemical signalling. The significances of bacterial colony patterns thus reside in a deeper understanding of prokaryotic biology and evolution and in experimental systems for studying self‐organization and morphoge

ISSN:0265-9247    

DOI:10.1002/bies.950170706

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe recombinational repair of chromosomal double‐strand breaks (DSBs) is of critical importance to all organisms, who devote considerable genetic resources to ensuring such repair is accomplished. InSaccharomyces cerevisiae, DSB‐mediated recombination can be initiated synchronously by the conditional expression of two site‐specific endonucleases, HO or I‐Scel. DNA undergoing recombination can then be extracted at intervals and analyzed. Recombination initiated by meiotic‐specific DSBs can be followed in a similar fashion. This type of ‘in vivobiochemistry’ has been used to describe several discrete steps in two different homologous recombination pathways: gene conversion and single‐strand annealing. The roles of specific proteins during recombination can be established by examining DNA in strains deleted for the corresponding gene. These same approaches are now becoming available for the study of recombination in both higher plants and animals. Physical monitoring can also be used to analyze nonhomologous recombination events, whose mechanisms appear to be conserved from y

ISSN:0265-9247    

DOI:10.1002/bies.950170707

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe proteins encoded by early region 1 A (E1A) of human adenoviruses (Ad) modulate the expression of both adenovirus genes and various host cell genes. With these transcription‐regulating properties the E1A proteins redirect the cell's metabolism, which enables them to induce oncogenic transformation in rodent cells. The E1A proteins modulate transcription by interacting both with gene‐specific and general cellular transcription factors. Various members of the AP‐1 and ATF/CREB families of transcription factors are targets for E1A‐dependent regulation, including cJun, the protein product of thec‐junproto‐oncogene. The E1A proteins modulate cJun‐dependent transcription both positively and negatively, and affect the activity as well as the expression levels of cJun. By increasing the phosphorylation status of cJun, E1A can stimulate transcription regulated by cJun/ATF2 heterodimers. In contrast, E1A inhibits the expression of various metalloproteases by interfering with the DNA‐binding capacity of cJun/cJun and cJun/cFos dimers, which might involve the association of E1A with the putative transcriptional coactivator p300. Since the ability of E1A to alter cJun‐dependent transcription correlates with its transforming capacity, interference with cJundependent transcription may be an essential step in E1A‐ind

ISSN:0265-9247    

DOI:10.1002/bies.950170708

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

年代:1995

数据来源: WILEY

摘要:

AbstractThebcl‐2gene product, a 25 kDa membrane protein residing at mitochondrial, microsomal and nuclear membrane sites within many cell types, is a broad and potent inhibitor of cell death by apoptosis. A family ofbcl‐2‐related genes with death‐inhibiting or ‐promoting activities has recently been described, indicating a potentially quite complex cell death regulatory network at the level of gene expression and protein‐protein interactions. The function ofbcl‐2may be to regulate a final common pathway in apoptosis. Current hypotheses suggest that oxidative stress, specific proteolytic activity or cell cycle control may be common elements in apoptosis through whichbcl‐2exerts its survival function. Based on the extent to which elements of apoptotic pathways overlap with non‐apoptotic cellular functions, the physiological role ofbcl‐2may also extend to other cellular processes such as differentiatio

ISSN:0265-9247    

DOI:10.1002/bies.950170709

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

年代:1995

数据来源: WILEY

摘要:

AbstractA fast growing family of ATPases has recently been highlighted. It was named the AAA family, for ATPases Associated to a variety of cellular Activities. The key feature of the family is a highly conserved module of 230 amino acids present in one or two copies in each protein. Despite extensive sequence conservation, the members of the family fulfil a large diversity of cellular functions: cell cycle regulation, gene expression in yeast and HIV, vesicle‐mediated transport, peroxisome assembly, 26S protease function etc. In addition, several members of this family can be found in the same organism (up to 17 inS. cerevisiae). The contrast between functional diversity and structural conservation of the module, from archaebacteria to mammals, suggests that it plays an essential, but as yet unknown, role at key points of the cellular machinery. Two (non‐exclusive) such possibilities are: (1) ATP‐dependent proteasome function and (2) ATP‐dependent anchorage of proteins. Finally, the basic biochemical activity of the AAA module is still a matter of speculation, and we propose that it acts as an ATP‐dependent prot

ISSN:0265-9247    

DOI:10.1002/bies.950170710

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

年代:1995

数据来源: WILEY

摘要:

AbstractUltraviolet (UV) radiation is a very common carcinogen in our environment, but epidemiological data on the relationship between skin cancers and ambient solar UV radiation are very restricted. In hairless mice the process of UV carcinogenesis can be studied in depth. Experiments with this animal model have yielded quantitative data on how tumor development depends on dose, time and wavelength of the UV radiation. In combination with epidemiological data, these experimental results can be transposed to humans. Comparative studies on molecular, cellular and physiological changes in mouse and man can further our fundamental understanding of UV carcinogenesis in man. This is likely to improve risk assessments such as those related to a stratospheric ozone depletion, and to yield well‐targeted intervention schemes, e.g. prescribing a specific drug or diet, for high‐risk individu

ISSN:0265-9247    

DOI:10.1002/bies.950170711

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

年代:1995

数据来源: WILEY