摘要:

AbstractNormal meiosis consists of a single round of DNA replication followed by two nuclear divisions. In the 1st division the chromosomes segregate reductionally whereas in the 2nd division they segregate equationally (as they do in mitosis). In certain yeast mutants, a single‐division meiosis takes place, in which some chromosomes segregate reductionally while others divide equationally. This autonomous segregation behaviour of individual chromosomes on a common spindle is determined by the centromeres they carry. The relationship between reductional segregation of a pair of chromosomes and their earlier recombinational history is also discusse

ISSN:0265-9247    

DOI:10.1002/bies.950150102

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

年代:1993

数据来源: WILEY

摘要:

AbstractRetinoic acid (RA), a derivative of vitamin A, is essential for normal mammalian development. Developmental abnormalities induced by RA excess and vitamin A deficiency are different even though they affect the same organ systems, and it is clear that there are intraembryonic tissue differences in the requirement for RA. The developmental functions of RA are mediated by its effects on gene expression. In the nucleus, two different forms of RA bind to and activate two families of nuclear receptors, which themselves co‐operate in initiating the transcription of target genes. In this article I propose that the amount of RA reaching the nucleus in different embryonic tissues is modulated by a mechanism involving three cytoplasmic binding proteins for retinol (CRBP I) and retinoic acid (CRABP I and II). Abnormalities of craniofacial development resulting from exposure of early neural plate stage embryos to RA excess have been studied in some detail; their initial stages involve alteration of both morphological development and the segment‐specific pattern of gene expression in the early hindbrain and its derived neural crest. This system is ideal for studying the relationships between retinoic acid receptors, retinoid binding proteins, and the development of genetic and morphological patt

ISSN:0265-9247    

DOI:10.1002/bies.950150103

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

年代:1993

数据来源: WILEY

摘要:

AbstractMany bacteria that cause disease have the capacity to enter into and live within eukaryotic cells such as epithelial cells and macrophages. The mechanisms used by these organisms to achieve and maintain this intracellular lifestyle vary considerably, but most mechanisms involve subversion and exploitation of host cell functions. Entry into non‐phagocytic cells involves triggering host signal transduction mechanisms to induce rearrangement of the host cytoskeleton, thereby facilitating bacterial uptake. Once inside the host cell, intracellular pathogens either remain within membrane bound inclusions or escape to the cytoplasm. Those living in the cytoplasm can further pirate the host actin system, using actin as a mechanism to facilitate movement within and between host cells. Organisms remaining within the vacuole have specialized mechanisms for intracellular survival and growth which involve additional communication with the host cell. Some of the processes involved in the various steps of facultative intracellular parasitism are discussed in the context of subverting the host cell cytoskeleton and signal transduction pathways for bacterial benefi

ISSN:0265-9247    

DOI:10.1002/bies.950150104

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

年代:1993

数据来源: WILEY

摘要:

AbstractAn increasing number of transcription factors both from prokaryotic and eukaryotic sources are found to bend the DNA upon binding to their recognition site. Bending can easily be detected by the anomalous electrophoretic behaviour of the DNA‐protein complex or by increased cyclization of DNA fragments containing the protein‐induced bend. Induction of DNA bending by transcription factors could regulate transcription in various ways. Bending may bring distantly bound transcription factors closer together by facilitating DNA‐looping or it could mediate the interaction between transcription factors and the general transcription machinery by formation of large nucleoprotein structures in which the DNA is wrapped around the protein complex. Alternatively, the energy stored in a protein‐induced bend could be used to favour formation of an open transcription complex or to dissociate the RNA polymerase in the transition from initiation to elongation. Modification of the bend angles and bending centers, caused by homodimerization or heterodimerization of transcription factors, may well turn out to be an important way to enlarge the range of interactions required for regulation of gene exp

ISSN:0265-9247    

DOI:10.1002/bies.950150105

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

年代:1993

数据来源: WILEY

摘要:

AbstractRNA editing is a newly described genetic phenomenon. It encompasses widely different molecular mechanisms and events. According to the specific RNA modification, RNA editing can be broadly classified into six major types. Type II RNA editing occurs in plants and mammals; it consists predominantly in cytidine to uridine conversions resulting from deamination/transamination or transglycosylation, although in plants other mechanisms have not been excluded. Apolipoprotein B mRNA editing is the only well‐documented editing phenomenon in mammals. It is an intranuclear event that occurs posttranscriptionally, coincident with splicing and polyadenylation. Recent observations indicate that the tissue‐ and sequence‐specific process is mediated by an enzyme that has separate domains for editing and sequence recognition. The presence of apolipoprotein B mRNA editing activity in tissues that do not produce the protein suggests that other RNAs may be edited and RNA editing may be a genetic phenomenon of general biological importance to the

ISSN:0265-9247    

DOI:10.1002/bies.950150106

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

年代:1993

数据来源: WILEY

摘要:

AbstractRhodopsin, upon activation by light, transduces the photon signal by activation of the G‐protein, transducin. The well‐studied rhodopsin/transducin system serves as a model for the understanding of signal transduction by the large class of G‐protein‐coupled receptors. The interactive form of rhodopsin, R*, is conformationally similar or identical to rhodopsin's photolysis intermediate Metarhodopsin II (MII). Formation of MII requires deprotonation of rhodopsin's protonated Schiff base which appears to facilitate some opening of the rhodopsin structure. This allows a change in conformation at rhodopsin's cytoplasmic surface that provides binding sites for transducin. Rhodopsin's 2nd, 3rd and putative 4th cytoplasmic loops bind transducin at sites including transducin's 5 kDa carboxyl‐terminal region. Site‐specific mutagenesis of rhodopsin is being used to distinguish sites on rhodopsin's surface that are important inbindingtransducin from those that function inactivatingtransducin. These observations are consistent with and extend studies on the action of other G‐protein‐coupled receptors and their interactions with their respec

ISSN:0265-9247    

DOI:10.1002/bies.950150107

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

年代:1993

数据来源: WILEY

摘要:

AbstractDuring the process ofE. colinucleotide excision repair, DNA damage recognition and processing are achieved by the action of theuvrA,uvrB, anduvrCgene products. The availability of highly purified proteins has lead to a detailed molecular description ofE. colinucleotide excision repair that serves as a model for similar processes in eukaryotes. An interesting aspect of this repair system is the protein complex's ability to work on a vast array of DNA lesions that differ widely in their chemical composition and molecular architecture. Here we propose a model for damage recognition in which the UvrB protein serves as the component that confers enhanced specificity to a preincision complex. We hypothesize that one major determinant for the formation of a stable preincision complex appears to be the disruption of base stacking interactions by DNA lesions.

ISSN:0265-9247    

DOI:10.1002/bies.950150108

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

年代:1993

数据来源: WILEY

ISSN:0265-9247    

DOI:10.1002/bies.950150109

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

年代:1993

数据来源: WILEY

摘要:

AbstractArabidopsis thaliana(Thale cress, Arabidopsis) is an ideal model organism for the molecular genetic analysis of many plant processes. The availability of a complete physical map would greatly facilitate the gene cloning steps in these studies. The small genome size of Arabidopsis makes the construction of such a map a feasible goal. One of the approaches to construct an overlapping library of the Arabidopsis genome takes advantage of the many mapped markers and the availability of Arabidopsis yeast artificial chromosome (YAC) libraries. Mapped molecular markers are used to identify corresponding YAC clones and thereby place them on the genetic map. Subsequently, these YAC clones provide the framework for directed walking experiments aimed at closing the gaps between the YAC contigs. Adopting this strategy, YAC clones comprising about 10% of the genome have been assigned to the top halves of Arabidopsis chromosomes 4 and 5. Extensive walking experiments in a 10 cM interval of chromosome 4 have resulted in two contiguous regions in the megabase size range.

ISSN:0265-9247    

DOI:10.1002/bies.950150110

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe transforming growth factors beta are a family of peptides which are involved in the regulation of cell growth and differentiation. It has been suggested that the loss of sensitivity to growth inhibition by endogenous TGF‐β may contribute to the process of carcinogenesis in epithelial systems. However, many breast cancer cells remain sensitive to the growth inhibitory effects of these peptides, suggesting that the local induction of TGF‐β could provide a pharmacological approach to chemoprevention. Triphenylethylene anti‐oestrogens, synthetic progestins and retinoids all offer potential as chemopreventative agents. A common feature of their mechanism of action is the ability to locally increase the production of the transforming growth facto

ISSN:0265-9247    

DOI:10.1002/bies.950150111

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

年代:1993

数据来源: WILEY