摘要:

AbstractA major barrier to recombination between bacterial species lies in the mismatch repair system, a complex of proteins that has evolved to proof‐read freshly replicated DNA. It now appears that a second system, involving an inducible DNA recombination, repair and mutagenesis pathway, also regulates interspecies recombination, but in a positive way, being required for recombination betweenEscherichia coliandSalmonella typhimurium(1). Thus the rate at which newly emerging species of bacteria diverge can be seen as a balance between a permissive state associated with inducible repair and recombination, and the proof‐reading of intermediates in the recombination pathway by the mismatch correction sys

ISSN:0265-9247    

DOI:10.1002/bies.950170902

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe development of the vertebrate skeleton is under complex genetic control, and good progress is being made towards identifying the genes responsible. A recent paper(1)contributes to this progress by describing transgenic mice in which the homeobox‐containingMHoxgene has been disrupted.MHox(−/−) mice have a range of skeletal defects, involving loss or shortening of structures in the skull, face and limb. Puzzling features of theMHox(−/−) mutation, which has similar effects on bones with very different embryological origins and yet spares other bones completely, may hold clues to the mechanisms that shape the skeleton.MHox(−/−) mice, used in conjunction with other skeletal mutants, will be important tools for exploring these mecha

ISSN:0265-9247    

DOI:10.1002/bies.950170903

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

年代:1995

数据来源: WILEY

摘要:

AbstractAlthough the genetics of dorsal‐ventral polarity which leads to mesoderm formation inDrosophilaare understood in considerable detail, subsequent molecular mechanisms involved in patterning the mesoderm primordium into individual mesodermal subtypes are poorly understood. Two papers published recently(1,2)suggest strongly that an inductive signal from dorsal ectoderm is involved in subdividing the underlying mesoderm, and present evidence that one of the signalling factors is Decapentaplegic (Dpp), a member of the bone morphogenetic protein subgroup of the Transforming Growth Factor‐β (TGF‐β) super family of p

ISSN:0265-9247    

DOI:10.1002/bies.950170904

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe mechanism of chromosome condensation is one of the classic mysteries of mitosis. A number of years ago, it was suggested that nonhistone proteins of the chromosome scaffold fraction might help chromosomes to condense, possibly by constructing a framework for the condensed structure. Recent results have shown that topoisomerase II and the SMC proteins, two abundant members of the scaffold fraction, are required for chromosome condensation and segregation during mitosis. Topoisomerase II is a well‐characterized enzyme. In contrast, nothing is yet known about the function of the SMC proteins. We summarize evidence suggesting that these proteins may be enzymes whose activity is somehow involved in the establishment and maintenance of mitotic chromosome morpholog

ISSN:0265-9247    

DOI:10.1002/bies.950170905

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

年代:1995

数据来源: WILEY

摘要:

AbstractMutations in DNA topoisomerase II are often correlated with drug‐resistance in tumor cell lines. Studies of topoisomerase II‐mediated drug‐resistance in various model systems, as well as the sequencing of such mutations from drug‐resistant tumors, have shed light on the functional domains of topoisomerase II, on how it interacts with inhibitors, and on the different mechanisms by which cells avoid the toxic effects of many clinically important anti‐tu

ISSN:0265-9247    

DOI:10.1002/bies.950170906

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

年代:1995

数据来源: WILEY

摘要:

AbstractHomeotic genes are subject to transcriptional silencing, which prevents their expression in inappropriate body regions. Here, we shall focus onDrosophila, as little is known about this process in other organisms. Evidence is accumulating that silencing ofDrosophilahomeotic genes is conferred by two types ofcis‐regulatory sequences: initiation (SIL‐I) and maintenance (SIL‐M) elements. The former contain target sites for transient repressors with a highly localised distribution in the early embryo and the latter for constitutive repressors that are likely to be present in all cells. We discuss how SIL‐I elements may cooperate with SIL‐M elements to promote formation of a silencing complex. We propose that this complex consists of specific non‐histone proteins, the so‐calledPolycombgroup proteins, and that it is anchored at SIL‐M elements and

ISSN:0265-9247    

DOI:10.1002/bies.950170907

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

年代:1995

数据来源: WILEY

摘要:

AbstractSmooth muscle cells have developed a contractile machinery that allows them to exert tension on the surrounding extracellular matrix over their entire length. This has been achieved by coupling obliquely organized contractile filaments to a more‐or‐less longitudinal framework of cytoskeletal elements. Earlier structural data suggested that the cytoskeleton was composed primarily of intermediate filaments and played only a passive role. More recent findings highlight the segregation of actin isotypes and of actin‐associated proteins between the contractile and cytoskeletal domains and raise the possibility that the cytoskeleton performs a more active function. Current efforts focus on defining the relative contributions of myosin cross‐bridge cycling and actin‐associated protein interactions to the maintenance of tension in smooth musc

ISSN:0265-9247    

DOI:10.1002/bies.950170908

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe lantibiotics are a rapidly expanding group of biologically active peptides produced by a variety of Gram‐positive bacteria, and are so‐called because of their content of the thioether amino acids lanthionine and β‐methyllanthionine. These amino acids, and indeed a number of other unusual amino acids found in the lantibiotics, arise following post‐translational modification of a ribosomally synthesised precursor peptide. A number of genes involved in the biosynthesis of these highly modified peptides have been identified, including genes encoding the precursor peptide, enzymes responsible for specific amino acid modifications, proteases able to remove the leader peptide, ABC‐superfamily transport proteins involved in lantibiotic translocation, regulatory proteins controlling lantibiotic biosynthesis and proteins that protect the producing strain from the action of its own lantibiotic. Analysis of these genes and their products is allowing greater understanding of the complex mechanism(s) of the biosynthesis of these uniqu

ISSN:0265-9247    

DOI:10.1002/bies.950170909

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

年代:1995

数据来源: WILEY

摘要:

AbstractEndosperm is emerging as a system for investigating the genetic control of wall placement and deposition in plant development. Development of endosperm progresses in distinct stages from a wall‐less syncytial stage to a cellular stage that is entirely typical of plant meristems where the division plane is predicted by a preprophase band of microtubules (PPB) and cytokinesis is completed by formation of a cell plate in association with a phragmoplast. Four developmentally different types of walls, each associated with a different microtubule system, are sequentially produced: (1) free growing walls deposited in the absence of mitosis and phragmoplasts; (2) walls guided by cytoplasmic phragmoplasts formed adventitiously in the absence of mitosis; (3) walls formed by interzonal phragmoplasts in a cell cycle that lacks PPBs; and (4) wall deposition driven by interzonal phragmoplasts in a cycle that includes PPBs. We are using methods of differential screening to isolate cDNA clones corresponding in temporal and spatial pattern to the types of wall development, and are studying mutants for clues to the genetic controls of wall developmen

ISSN:0265-9247    

DOI:10.1002/bies.950170910

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

年代:1995

数据来源: WILEY

摘要:

AbstractSex‐determining mechanisms appear to be very diverse in invertebrates. Haplodiploidy is a widespread mode of reproduction in insects: males are haploid and females are diploid. Several models have been proposed for the genetic mechanisms of sex determination in haplodiploid Hymenoptera. Although a one‐locus multi‐allele model is valid for several species, sex determination in other species cannot be explained by any of the existing models. Evidence for and predictions of two recently proposed models are discussed. Some genetic and molecular approaches are proposed to study sex determination in Hymeno

ISSN:0265-9247    

DOI:10.1002/bies.950170911

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

年代:1995

数据来源: WILEY