摘要:

SummaryThe classical analyses of phage morphogenesis provide experimental paradigms for dissecting other assembly pathways. A new set of results, derived from examination of the quantitative controls of tubulin levels and microtubule assembly inSaccharomyces cerevisiae, evokes the balance of components’ hypothesis. These results show that balanced levels of the tubulin proteins are crucial for microtubule assembly. Imbalances leading to excess beta tubulin have far more deleterious consequences than those leading to excess alpha tubulin, including dramatic cellular toxicity, quantitative depolymerization of cellular microtubules, and self‐aggregation of the excess beta tubulin. These and other results suggest that beta tubulin may possess a unique ability to interact with a component of microtubule nucleating sites, and provide a rationale for the universal polarity of nucleated microtubu

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01515.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryElongation factor Tu (EF‐Tu), the most abundant protein inEscherichia coli, is a guanine nucleotide‐binding protein that in the ‘on’ state acts as a carrier of amino acyl‐tRNA to the ribosome. Our knowledge of this essential component of translation has brought substantial progress in the past decade thanks to the co‐ordinated application of biochemical, physico‐chemical and genetic methods. Crystallographic analysis at 2.6 Å resolution and site‐directed mutagenesis have revealed structural and functional similarities between the guanine nucleotide‐binding domains of EF‐Tu and human H‐rasp21 protein. The regulation of the expression of the two EF‐Tu‐encoding genes inE. coli, particularly that oftufB, has been shown to involve diverse mechanisms. Several aspects of the functions of EF‐Tu in the elongation cycle have been reinvestigated, leading to new insights. These studies have emphasized the manifold aspects of the mechanisms regulating the activity of

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01516.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryOne of the most intriguing questions posed by bacterial spore formation concerns the establishment of cell‐specific gene expression in the prespore and mother cell. Recent results now suggest that sigma factors, in addition to their temporal roles in the control of gene expression, may also be the key determinants of differential gene expression during sporulation inBacillus subtilis.The genes encoding two sporulation‐specific sigma factors, σEand σF, are expressed soon after the initiation of sporulation, before the formation of the spore septum that separates the prespore and mother cell compartments, it now appears that σEand σFdirect transcription only after septation and then In a specific cell type, suggesting that the segregation of the sigma activities after septation is a key event in the establishment of differential gene expression. The mechanism responsible for this segregation is complex, involving at least seven other gene products. We discuss possible models for the interactions between the sigma factors and the establishment of cell‐specific tran

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01517.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryUp to 80% of faecalEscherichia coilstrains are able to produce type 1 pili. These filamentous bacterial surface organelles, which mediate mannose‐sensitive attachment to mammalian epithelial cells, are also conserved throughout the Enterobacteriaceae. As a potential explanation for their prevalence among intestinal isolates of enteric bacteria, it has been widely speculated that type 1 pili are important for adherence to the host's intestinal mucosa. However, conclusive evidence for this idea is lacking, and there are reasonable grounds for doubting such an effect. Permanent interruption of type 1 pillation in previouslypil+E. coli(by directed mutagenesis ofpilA, the gene coding for the major structural subunit of type 1 pili) does not diminish the density of intestinal colonization in individual animals. Rather, as we demonstrate here, this lesion results in a dramatic decrease in transmission ofE. coliK1 from experimentally colonized neonatal rats to their littermates. The enhanced communicability associated with type 1 pillation suggests a heretofore unrecognized explanation for the prevalence of type 1 pili among intestinalE. coli; one that does not necessarily require the direct action of these organelles at the intestinal mucos

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01518.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryA novel gene fusion approach which may be of more general use has been developed for investigating the function of calmodulin in the budding yeastSaccharomyces cerevisiae.By fusing a portion of theStaphylococcus aureus spagene (encoding protein A) toCMD1, theS. cerevisiaegene encoding calmodulin, we have generated a yeast calmodulin with an affinity tag able to bind immunoglobulins. The chimaeric protein A–calmodulin (ProtA–CaM) polypeptide functionsin vivoand shows Ca2+‐dependent binding to calmodulin target proteins. Thespa–CMD1fusion has been used (i) to prepare (by affinity chromatography) a fraction of yeast proteins which interact with calmodulin, (ii) to isolate genes encoding calmodulin target proteins by direct screening of an expression library, and (iii) to visualize calmodulin‐binding proteins in crude extracts by Western blot

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01519.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryThe location of FtsQ, anEscherichia coliprotein essential for cell division, is, under physiological conditions, in the cytoplasmic membrane facing towards the periplasmic space. An amino‐proximal hydrophobic domain is required for FtsQ to reach its location and for its activity in the cell. Overexpression of modified forms of FtsQ is deleterious for the cel

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01520.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryOuter‐membrane blebs from two serum‐susceptible and two serum‐resistant strains ofNeisseria gonorrhoeaewere characterized. In general, bleb surfaces resembled cell surfaces, but there were qualitative and quantitative protein differences in blebs released by serum‐susceptible and serum‐resistant strains. Relative to blebs from serum‐resistant strains, blebs from serum‐susceptible strains expressed reduced amounts of major outer‐membrane proteins I and III, and little if any 68 000 Dalton outer

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01521.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryWe studied the interaction of normal human serum immunoglobulins with outer‐membrane bleb antigens ofNeisseria gonorrhoeae.Gonococcal 68000 Dalton and Lip (H.8 antigen) outer‐membrane proteins were recognized by normal human serum immunoglobulins in blebs from serum‐resistant strains, but not in blebs from serum‐susceptible strains. The addition of blebs from a serum‐resistant strain to bactericidal assays resulted in significantly greater inhibition of serum killing than the addition of blebs from a serum‐susceptible strain. Our results indicate that blebs from two serum‐resistant gonococcal strains have an enhanced ability to bind and remove cell‐targeted bactericidal factors, and that outer‐membrane bleb‐bing may contribute

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01522.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryTheexcCmutants ofEscherichia coliare hypersensitive to drugs such as cholic acid and release periplasmic proteins Into the extracellular medium. A 1884 bp fragment carrying theexcCgene was isolated and sequenced. It contains the 3′ end of thetolBgene which maps at min 17 on theE. collmap and an open reading frame which encodes the 18748 Da ExcC protein. The protein is composed of a hydrophobic region of 22 residues and displayed an overall hydrophilic configuration. It was shown that the ExcC protein is indeed the PAL (peptidoglycan‐associated lipoprotein) described by Mizuno (1979). Thepalgene had not yet been characterized on theE. colilinkage map since no obvious phenotype could be identified for mutations in this gene. A topologic analysis of the PAL protein using PAL–PhoA translational fusions showed that PAL is associated with the outer membrane only by itsN‐terminal moiety. The carboxy‐terminal part of the protein is necessary for correct interaction of PAL with the peptidogly

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01523.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryExpression of the Cob operon inSalmonella typhimuriumis repressed by cobalamin (Cbl). Here it is shown that Cbl repression is mediated by a post‐transcriptional regulatory mechanism that requires sequences within the leader and the first translated open reading frame, thecbiAgene. Transcriptional and translational Cob::lacZfusions containing various lengths of Cob DNA were analysed. In a translational Cob::lacZfusion 407 bp of leader sequence (+69 to +476) was sufficient to confer normal repression. However in a transcriptional Cob::lacZfusion a 618 bp region (+69 to +687) was required for normal repression. This 618 bp region included sequences in the leader as well as sequences within thecbiAgene. Point mutations which resulted in loss of repression control were isolated and shown to be clustered in the leader sequence (+257 to +380). This region contains a putative hairpin‐loop structure which we propose functions as an RNA operator site for a vitamin B12‐responsive repressor pr

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01524.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY