摘要:

SummaryTheYersinialow‐Ca2+response (LCR) is a regulatory response in which a set of plasmid‐borne operons is transcriptionally regulated at 37°C in response to the presence or absence of mM concentrations of Ca2+. LCR‐regulated operons encode secreted proteins with regulatory and virulence roles as well as non‐secreted regulatory proteins and components of the secretion machinery. Downregulation by Ca2+is imposed by a signalling cascade that includes secreted proteins and possibly also components of the secretion system and is hypothesized to act on membrane‐bound inductive components. An important rote in LCR induction is played by LcrD, an inner‐membrane protein with homologues in several virulence‐associated and flagella assembly‐related systems in diverse bacterial species. The mechanism of signal transduction in response to Ca2+is not known, and the proteins that bind DNA to downregulate transcription have not

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01644.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryOur knowledge of the different biological roles of tRNA modification has increased considerably in recent years. Not only have we learned about how modified nucleosides affect the performance of tRNA in translation, but also how they influence regulation of intermediary metabolism, antibiotics production, gene expression in eukaryotic viruses, cell division, cell‐cycle control, u.v. sensitivity, and mutation frequency. This review summarizes our current understanding of the role of tRNA modificatio

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01645.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryThe transposon Tn5expresses a gene,ble, whose product increases the viability ofEscherichia coliand also confers resistance to the DNA‐cleaving antibiotic bleomycin and the DNA‐alkylating agent ethyl‐methanesulphonate. We find that the Ble protein induces expression of an alkylation inducible gene,aidC, and that both the AidC gene product and DNA polymerase I are required for Ble to confer bleomycin resistance. These findings support models in which Ble enhances DNA repair and suggest that Tn5confers a fitness advantage to the host bacterium by increasing the repair of spontaneous DNA lesions. Such co‐operation between a transposon and its host suggests that Tn5is a symbiotic rather than a selfish DNA

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01646.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryMycobacterial cell wall functions as an effective permeability barrier, making these bacteria resistant to most antibacterial agents. It has been assumed that this low permeability was due to the presence of a large amount of unusual lipids in the cell wall, but it was not known how these lipids are able to produce such an exceptional barrier. We report here the first experimental evidence on the physical arrangement of these lipids based on X‐ray diffraction studies of purifiedMycobacterium chelonaecell wall, a result suggesting that the hydrocarbon chains of the cell‐wall lipids are arranged predominantly in a direction perpendicular to the cell wall surface, probably producing an asymmetric bilayer struct

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01647.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryMultimer formation reduces plasmid copy number and is an established cause of segregational instability. Nevertheless, it is difficult to rationalize observations that low levels of dimers can cause severe instability, if we assume they are distributed evenly in cell populations. We report here that dimer distribution is in fact heterogeneous in recombination‐proficient strains. Most cells in the population contain only monomers; dimers are confined to a small sub‐population from which plasmid‐free daughters arise at high frequency. In arec+culture where 4% of pBR322 molecules are dimers, more than half are in dimer‐only cells. We show that this situation is inevitable because dimers replicate at twice the rate of monomers. Runaway multimerization is avoided because dimer‐containing cells grow more slowly than their monomer‐containing counterparts. A computer simulation is used to show how dimers proliferate after formation by homologous recombination. The equilibrium concentration of dimers is proportional to the inter‐plasmid recombination rate and is essentially independent of the rate at which homologous recombination converts dimer

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01648.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryThe alkane hydroxylase system ofPseudomonas oleovorans, which catalyses the initial oxidation of aliphatic substrates, is encoded by three genes. One of the gene products, the alkane hydroxyiase AlkB, is an integral cytoplasmic membrane protein. Induction leads to the synthesis of 1.5–2% AlkB relative to the total cell protein, both inP. oleovoransand in recombinantEscherichia coliDH1. We present a study on the Induction and localization of the alkane hydroxylase inE. coliW3110, which appears to be an interesting host strain because it permits expression levels of AlkB of up to 10–15% of the total cell protein. This expression level had negative effects on cell growth. The phospholipid content of such cells was about threefold higher than that of wild‐type W3110. Freeze‐fracture electron microscopy showed that induction of thealkgenes led to the appearance of membrane vesicles in the cytoplasm; these occurred much more frequently in cells expressingalkBthan in the negative control, which contained all of thealkgenes except foralkB.Isolation and separation of the membranes of cells expressingalkBby density gradient centrifugation showed the customary cytoplasmic and outer membranes, as well as a low‐density membrane fraction. This additional fraction was highly enriched in AlkB, as shown both by SDS‐PAGE and enzyme activity measurements. A typical cytoplasmic membrane protein, NADH oxidase, was absent from the low‐density membrane fraction,alkBexpression in W3110 changed the composition of the phospholipid headgroup in the membrane, as well as the fatty acid composition of the membrane. The major changes occurred in the unsaturated fatty acids: C16:1and C18:1increased at the expense of C17:0cy

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01649.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryA transposon (Tn5‐SC) was constructed that can be used to quantify genetic deletions or amplifications. This transposon was used to evaluate the genomic stability ofXanthomonas campestrispv.campestrisNRRL B1459 and we found that the genome of this bacterium is as stable as other Gram‐negative bacteria or even more stable. Homologous recombination between plasmid sequences was determined in strain NRRL B1459 and was found to occur at a similar level to that reported for other Gram‐negative bacteria. We report here that inX.c.c.NRRL B1459 there is no straightforward correlation between the occurrence of genetic rearrangements and frequency of homologous recombination. These data are discussed with respect to the reported instability of strain NRRL B1459 for xanthan gum produ

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01650.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryInduction ofcat‐86 translation results from the stalling of a ribosome at a discrete location in the leader region of the transcript. Stalling destabilizes an adjacent region of secondary structure that sequesters thecat‐86 ribosome binding site, thereby activatingcat‐86 translation. Two well characterized antibiotics, chloramphenicol and erythromycin, inducecat‐86 by stalling a ribosome at the appropriate leader site. Here we demonstrate differences between the two antibiotics with respect to induction. First, induction by chloramphenicol is dependent on nucleotides in the leader sequence that are different from those necessary for erythromycin induction. Second, variants ofBacillus subtilisthat are chloramphenicol resistant because of chromosome mutations permitcat‐86 induction by chloramphenicol, whereas erythromycin‐resistance host mutations block or greatly reducecat‐86 induction by erythromycin. Third, selected strains ofB. subtilisbearing alterations in proteins of the 50S ribosomal subunit interfere withcat‐86 induction by chloramphenicol, yet these strains are chloramphenicol sensitive. Lastly, induction by chloramphenicol is not reversed by removal of the antibiotic whereas erythromycin induction is reversible. The data indicate that chloramphenicol induction results from an effect of the drug that is not identical to its role as a general inhibitor of ribosome elongation. Induction by erythromycin, on the other hand, could not be distinguished from its anti

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01651.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryA 3.2 kb chromosomal DNA fragment which complements the defects in a series of twelvemoa::Mucts insertion mutants has been sequenced. Five open reading frames (ORFs) were identified and these are arranged in a manner consistent with their forming an operon. The encoded proteins (MoaA‐MoaE) have predicted molecular weights of 37346, 18665, 17234, 8843 and 16981 respectively. Examination of subclones of the whole locus in an expression system demonstrated the predicted products.N‐terminal amino acid sequences for themoa A, B, CandEproducts confirmed the translational starts. Genetic analysis distinguished four classes ofmoamutants corresponding to genesmoaA, C, DandE.Potential promoter sequences upstream ofmoaAand a possible transcription termination signal have been identified. Genetic analysis of thechlA1andchlMmutants, which have been biochemically characterized as defective in molybdopterin biosynthesis, indicates that these carry lesions inmoaAandmoaDrespectively. Themoalocus is orientated clockwise at 17.7 minutes in the chromos

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01652.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

SummaryBacterial exopolysaccharide (EPS) and lipopolysaccharide (LPS) molecules have been shown to play important roles in plant‐bacterium interactions. Here we have demonstrated that thefix‐23 loci, which compensate forexomutations during symbiotic nodule development, are involved in the production of a novel polysaccharide that is rich in 3‐deoxy‐Dmanno‐2‐octulosonic acid (Kdo) but is not the classical LPS. This molecule is likely to be a surface antigen since antiserum to wholeRhizobium meliloticells reacts strongly with it, and since mutations infix‐23 result in an inability to produce this polysaccharide and to bind bacteriophage 16‐3. It is likely that this Kdo‐rich polysaccharide is analogous to certainEscherichia coliK‐antigens which are anchored to the membrane via a phospholipid moiety. DNA sequence analysis of one gene cluster of this region revealed that the predicted protein products of six genes exhibit a high degree of homology and similar organization to those of the rat fatty acid synthase multifuncti

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1993.tb01653.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY