摘要:

SummaryThe DNA in dormant spores ofBacillusspecies is associated with α/β‐type small, acid‐soluble proteins (SASP), which are double‐stranded DNA‐binding proteins whose amino acid sequence has been highly conserved in evolution.In vitrothese proteins bind most strongly to DNA which readily adopts an A‐like conformation, as binding of α/β‐type SASP causes DNA to assume an A‐like conformation. As predicted by this conformational change in DNA, binding of α/β‐type SASP to relaxed but covalently closed plasmid DNA results in the introduction of a large number of negative supercoils. Associated with the conformational change in DNA brought about by α/β‐type SASP binding is a change in its photochemistry such that ultraviolet irradiation does not generate pyrimidine dimers, but rather a thyminyl‐thymine adduct termed spore photoproduct (SP). The latter two properties of DNA complexed with α/β‐type SASPin vitroare similar to those of DNA in dormant spores ofBacillusspecies in which: (i) plasmid DNA has a much higher number of negative supercoils than plasmid in growing cells; and (ii) ultraviolet irradiation produces SP and no pyrimidine dimers, while only pyrimidine dimers are formed in growing cells. During sporulation these changes in the properties of spore DNA take place in parallel with synthesis of α/β‐type SASP, and the magnitude of the changes is greatly reduced in mutants that make low amounts of these proteins. A straightforward interpretation of these data is that DNA in dormant spores ofBacillusspecies is in an A‐like conformation. DNA in an A‐like conformation is also present in growing cells with high α/β‐type SASP levels. However, the presence of th

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01501.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryBiological processes such as transcription are expected to generate local variations in DNA super‐coiling. The existence of localized supercoiling was recently demonstrated inEscherichia coliby using the supercoil‐driven B‐to‐Z transition as a super‐helicity probe. This new methodology is described and its extension to other biological systems

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01502.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryThe major phosphate‐repressible acid phosphatase (APase) ofSaccharomyces cerevisiae, a cell wall glycoprotein, has been extensively used as a reporter protein to analyse successive steps in the yeast secretory pathway. In contrast to other yeast secretory proteins, APase can still be translocated into the endoplasmic reticulum (ER) even when it is made without its signal peptide. This property illustrates the permissiveness of targeting to the ER in yeast. Studies on APase‐containing hybrid proteins have provided some of the evidence that specific soluble factors must interact with secretory proteins prior to their translocation across the ER membrane. A systematic analysis of mutations affecting the sequence of the APase signal peptide cleavage site demonstrated that cleavage occurs only when the last amino acid of the signal sequence is small and neutral. This was one of the first studies to verify the requirements for signal peptidase cleavage that had previously only been predicted from statistical analysis. Studies performed either with inhibitors of glycosylation or with mutant APases demonstrated the critical role of core glycosylation for APase folding, which is essential for efficient transport beyond the ER. Following the fate of particular modified APases along the secretory pathway provided insights into some general properties of the secretory apparatus and illustrated the specific requirements for a given protein during its intracellular traf

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01503.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryTranscription elongation catalysed by DNA‐dependent RNA polymerase does not occur at a constant rate. Instead, during the transcription of many genes pausing occurs at defined template positions. Pausing is known to be influenced by the intracellular NTP concentration, the secondary structure of the growing transcript or by transcription factors like NusA. We have investigated the effects of the template topology of transcriptional pauses in the presence and absence on purified NusA protein. Taking advantage of a method for quantifying transcriptional pauses we have studied pausing behaviour duringin vitrotranscription of the early region of a plasmid‐encoded ribosomal RNA operon. Plasmid templates with different super‐helical densities (σ between +0.0017 and ‐0.055) were employed in transcription elongation assays. If linearized or relaxed templates are used, some of the characteristic pauses can no longer be detected. For the stronger pauses we could demonstrate a direct correlation between pause strength and the negative superhelical densities of the templates used. This correlation is observed regardless of whether or not pauses are dependent upon NusA. Changes in the average transcription elongation rate, caused by variations in the NTP concentration or the temperature, do not appear to have a comparable effect on transcription pausing. The results are consistent with the assumption that the template topology has a regulatory function in transcription elongation of rRNA genes inEscheric

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01504.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryTumour necrosis factor alpha (TNF‐α) has been shown to be the principal mediator of Gram‐negative bacterial endotoxin‐induced shock. Nevertheless, evidence suggests that TNF‐α plays a beneficial role in controlling bacterial infections when multiplication of the microorganism is required to kill the host. Using an infant rat model ofNeisseria meningitidisinfection, we found that blood TNF‐α concentration reaches a peak three hours after intraperitoneal injection of 3 × 106bacteria. Thereafter, the level of TNF‐α decreased and was undetectable six to eight hours after infection. A correlation was observed between the magnitude of initial TNF‐α response and a fatal outcome. Pretreatment of the animals with polyclonal anti‐TNF antiserum significantly reduced mortality relative to animals pretreated with control serum. However, pretreatment of animals with anti‐TNF antibody did not alter the bacterial invasion of the cere‐brospinal fluid. Injection of heat‐killed bacteria did not cause death and induced lower TNF‐α levels than the same number of live bacteria. This excludes the possibility that the role of TNF‐α is to mediate a shock induced by the endotoxin component of the bacterial inoculum. These results indicate that TNF‐α has a deleterious effect in this model of bacteraemia. Identification of the critical factors that determine the action of TNF‐α during lethal bacteraemia will lead to a better understanding of these diseases and the development

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01505.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryThe rote of SecB protein in the export of the precursor of outer membrane protein PhoE and mutant forms of this precursor was studiedin vitro.When synthesized in the absence of SecB, translocation‐competent prePhoE was observed post‐translationally, but addition of SecB was required for efficient translocation into inner membrane vesicles. The translocation competency ofin vitrosynthesized prePhoE diminished with a similar half‐life during incubations in the presence or absence of SecB. The loss of translocation competency of prePhoE, synthesized in the presence of SecB, was not due to dissociation of prePhoE–SecB complexes as could be demonstrated in co‐immunoprecipitation experiments with anti‐SecB serum. Apparently, SecB does not maintain the translocation‐competent conformation of prePhoE, but is mainly required for efficient targeting of this precursor to the exp

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01506.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryThe Incl1 conjugative plasmid Collb‐P9 carries apsiBgene that prevents induction of the SOS response in host bacteria. This locus is located 2.5 kb downstream of thessb(single‐stranded DNA‐binding protein) gene in the leading region. This portion of Collb is strikingly similar to part of the leading region of the otherwise distinct F plasmid. Expression ofpsiBandssbis increased when the host cell is exposed to an SOS‐inducing treatment or the Collb transfer system is derepressed. Moreover, expression of both genes on a derepressed plasmid is strongly enhanced in conjugatively infected recipient cells. Carriage of thepsiBgene by Collb is shown to prevent a low level of SOS induction following conjugation. PlasmidssbandpsiBgenes may function to promote installation of the replicon in the n

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01507.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryWe show that the 53‐nucieotide RNA molecule encoded by genedicFblocks cell division InEscherichia coliby inhibiting the translation offtsZmRNA. Such a role fordicFhad been predicted on the basis of the complementarity of DicF RNA with the ribosome‐binding region of theffsZmRNA. An analysis offtsZexpression at its chromosomal locus, and of anftsZ–lacZtranslational fusion controlled by promotersftsZ1pandftsZ2ponly, indicates thatftsZis not autoregulated. Partial inhibition of FtsZ synthesis leads to increased cell size. However, the number of FtsZ molecules per cell can be reduced threefold without affecting the division rate significantly. Our results suggest that septation is not triggered by a fixed number of newly synthesized FtsZ molecules per

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01508.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryThe cell‐cycle parameters of anEscherichia colistrain expressing essential division geneftsZat one‐fifth of its normal level, because of antisense regulation by DicF RNA, have been analysed. Inhibition of FtsZ expression affects neither the generation time nor the replication initiation mass, the C period, or the constriction period, but it does dramatically retard the initiation of constriction relative to replication termination. Separation of the nucleoids is equally postponed, indicating that division is not coupled to termination of replication, but to partitioning. The severe inhibition of nucleoid separation by DicF RNA, and its suppression by overproduction of FtsZ, suggest a role for FtsZ in the control of separation, and consequently in the coupling of separation and division. We suggest that the normal pattern of nucleoid separation previously found in cells deficient inftsZfunction was a consequence of the loss of a negative effect exerted by FtsZ on separation. In agreement with this view, we find that nucleoid separation is temporarily inhibited after arrest of FtsZ synthesis, but is later resumed as FtsZ is further diluted into the elongating filame

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01509.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryGenes and their organization are conserved in the replication origin region of the bacterial chromosome. To determine the extent of the conserved region in Gram‐positive and Gram‐negative bacteria, which diverged 1.2 billion years ago, we have further sequenced the region upstream from thednaAgenes inBacillus subtilisandPseudomonas putida.Fifteen open reading frames (ORFs) and 11 ORFs were identified in the 13.6 kb and the 9.8 kb fragments inB. subtilisandP. putida, respectively. Eight consecutiveP. putidagenes, except for one small ORF (homologous to gene9KofEscherichia coli)in between, are homologous in sequence and relative locations to genes inB. subtilis.Altogether, 12 genes and their organization are conserved inB. subtilisandP. putidain the origin region. We found that the conserved region terminated on one side after theorf290inP. putida (orf282inB. subtilis).In theB. subtilischromosome, five additional ORFs were found in between the conserved genes, suggesting that they are added after Gram‐positive bacteria were diverged from the Gram‐negative bacteria. One of the ORFs is a duplicate of the conserved gene. The third non‐translatable region containing multiple repeats of DnaA‐box (second in the case ofP. putida)was found flankinggidAin both organisms. This result shows clearly thatE. coli oriCand flanking genesgidAandgidBhave been translocated by the inversion of some 40

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01510.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY