摘要:

SummaryA variety of reports describe shifts in the environment which cause a corresponding change in the measured linking number of plasmid DNA isolated from bacterial cells. This change in linking number is often attributed to a change in superhelical density. This, coupled with the observation that transcription is often dependent upon the superhelical density of the DNA template seenin vitro, has led to the suggestion that superhelical density may control expression of certain genes. However, since many environmental changes could, in principle, influence DNA twist itself, then the measured differences in linking number, δLk, may simply be a consequence of variation in twist according to the relationship δLk=δTw+δWr, where δTwand δWrare changes in twist and writhe, respectively. In fact, we show that when an environmental change causes a change in the helical pitch of the DNA, and if the superhelical density of DNA is regulated to remain constant according to the homeostatic model of Menzel and Gellert, then δLkδTw.We have found that there are a number of published reports describing variation in promoter activity as a function of linking number that can be explained by considering twist. We suggest that there are classes of σ70promoters whose ability to be recognized by RNA polymerase is exquisitely sensitive to the relative orientation of the ‐35 and ‐10 regions, and environmental conditions can control this relative orientation by changing DNA twist. TherecAandproUpromoters which are activated by cold shock and osmotic shock, respectively, behave as if they are twist‐sensitive promoters. Consideration of DNA twist can also account for the change in activity of a number of other promoters when they are placed in bacterial strains defective in either DNA gyrase or

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01358.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummarySummary TheSaccharomyces cerevisiaePOT1 gene is, as are other yeast peroxisomal protein genes, inducible by fatty acids and repressible by glucose. We have now found that it is also induced during the stationary phase of the culture. To investigate these three regulatory circuits, we have studied the mRNA levels of regulatory mutants as well as the changes in chromatin structure upon gene activation. We conclude that the regulation of transcriptional activity in glucose repression, oleate induction, and stationary phase induction follow different molecular mechanisms. We suggest that this multiplicity of regulatory mechanisms may represent a general rule for the yeast peroxisomal protein genes.

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01359.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryThe putative stationary‐phase sigma factor (σS) encoded byrpoSis essential for giycogen synthesis, but is not required for the transcription ofglgCandglgA, which encode ADP‐glucose‐pyrophosphorylase and glycogen synthase, respectively. Using a mini‐Mu random chromosomal library and a screen for glycogen overproduction, we identified a novel gene (glgS) involved in glycogen synthesis.glgSmaps at 66.6 min (3247 kb) on the chromosome and constitutes a mono‐cistronic operon. It encodes a hydrophilic and highly charged small protein, with a molecular weight of 7886, which is strongly expressed in minicells. Experiments with single‐copy chromosomalglgS::lacZgene fusions indicated thatglgSexpression is controlled by σSas well as by cAMP. Two transcriptional start sites were mapped in the upstream regulatory region ofglgS.TheglgSp1 transcript was absent in acyamutant, whereas anrpoSmutant did not synthesize theglgSp2 transcript. Although glycogen synthesis is strongly stimulated by overproduction of GlgS and is inhibited by aglgSnull mutation,glgSdoes not affect the expression of theglgCAPoperon. Its potential role in the metabolic control of glycogen synthesis is discussed. Also, evidence is presented to show that the amount of glycogen accumulatedin vivoin early stationary‐phase cells is mainly determined by σS‐controlled gene expression and allosteric activation of GlgC, whereas the absolute levels of expression ofglgCAPas well as the intracellular concentration of cAMP are o

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01360.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryThe PulO protein required for extracellular secretion of pullulanase byKlebsiella oxytocais known to be highly homologous to two type IV prepilin peptidases, namely XcpA(PilD) (Pseudomonas aeruginosa) and TcpJ (Vibrio cholerae). The predicted prepilin peptidase activity of PulO was confirmed by showing that it could correctly process the product of the clonedpilE.1type IV pilin structural gene fromNeisseria gonorrhoeaeinEscherichia coli.TheP. aeruginosaprepilin peptidase and another putative prepilin peptidase, ComC fromBacillus subtilis, also processed prePilE. Subcellular fractionation showed that thepilEgene product that had been processed by PulO remained associated with the cytoplasmic membrane, as did the unprocessed precursor. PulO was also shown to process three of the four prePilE–PhoA hybrids tested. Southern hybridization experiments suggest that aPulOhomologue is present in theN. gonorrhoeaechromosom

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01361.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryLinked genes encoding two outer membrane proteins (p76 and a family of proteins, p120) of the bovine pathogen,Haemophilus somnus, were investigated. The p120 group was previously shown to have immunoglobulin‐binding activity and to react with polyclonal antiserum specific for a 270 kDa antigen (p270) which also had immunoglobulin Fc‐binding activity. By Western blotting we showed that the p76 antigen also reacted with this antiserum. The p270, p120, and p76 antigens were undetectable in four serum‐sensitive isolates from asymptomatic carriers but were present in the two serum‐resistant virulent strains tested. Genes for p120 and p76 were subcloned on non‐overlapping pUC plasmids from a cosmid (pHS1) originally cloned from a serum‐resistant strain. InEscheriehia coli, plasmid pHS138 expressed p76, while the p120 antigens were produced by pHS140. Southern blots of DNA from the above six strains ofH. somnususing probes derived from pHS1 subclones showed that a 13.4kb sequence was missing from the four serum‐sensitive strains, but not the two serum‐resistant strains. This segment included most of the insert in pHS138 and all of the pHS140 insert. The data indicate that p76 and the p120 proteins are absent from serum‐sensitive strains because the coding sequences are missing, raising the possibility of insertion of these genes into the chromosome of both serum‐resistant strains, or deletion from the four seru

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01362.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryPneumocystis cariniicauses life‐threatening pneumonia in T‐lymphocyte‐immunodeficient subjects in transplant and oncology units or with acquired immune deficiency syndrome (AIDS). Recent DNA homology studies showP. cariniito be a fungus. To investigate the biology and epidemiology of this parasite further, we elected to determine for it a more precise taxonomic assignment within the fungal kingdom. We screened a wide range of organisms representing the major orders of fungi using DNA amplification and subsequently sequenced a portion of the mitochondrial gene encoding the large subunit ribosomal RNA. Our data show that the opportunistic pulmonary pathogenP. cariniiis closely related to the ustomycetous red yeast fungi, a group which includes organisms that are extensively distributed throughout the environment and which release many widely dispersed airborne s

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01363.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryIn response to nitrate availability,Escherichia coliregulates the synthesis of a number of enzymes involved in anaerobic respiration and fermentation. When nitrate is present, nitrate reductase (narGHJI) gene expression is induced, while expression of the DMSO/TMAO reductase (dmsABC, fumarate reductase (frdABCD)and fermentation related genes are repressed. ThenarLandnarXgene products are required for this nitrate‐dependent control, and apparently function as members of a two‐component regulatory system. NarX is a presumed sensor‐transmitter for nitrate and possibly molybdenum detection. The presumed response‐regulator, NarL, when activated by NarX then binds at the regulatory DNA sites of genes to modulate their expression. In this study a third nitrate regulatory gene,narQ, was identified that also participates in nitrate‐dependent gene regulation. Strains defective in eithernarQornarXalone exhibited no nitrate‐dependent phenotype whereas mutants defective in bothnarQandnarXwere fully inactive for nitrate‐dependent repression or activation. In all conditions tested, this regulation required a functionalnarLgene product. These findings suggest that thenarXandnarQproducts have complementary sensor‐transmitter functions for nitrate detection, and can work independently to activate NarL, for eliciting nitrate‐dependent regulation of anaerobic electron transport and fermentation functions. ThenarQgene was cloned, sequenced, and compared with thenarXgene. Both gene products are similar in size, hydrophobicity, and sequence, and contain a highly conserved histidine residue common to sensor–t

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01364.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryWe have isolated a gene encoding a previously unreported class of trypanosomatid cysteine proteinase (CP) from the protozoan parasiteLeishmania mexicana.The single‐copy gene (Imcpa) has several unusual features that distinguish it from CP genes cloned from the related speciesTrypanosoma bruceiandTrypanosoma cruzi.These include a shorterC‐terminal extension of only 10 amino acids and a three‐amino‐acid insertion, GlyValMet, close to the predictedN‐terminus of the mature protein. Northern blot analysis showed that the gene is expressed in all life‐cycle stages but at higher levels in the amastigote stage in the mammal and in stationary phase promastigote cultures which contain the infective meta‐cyclic form of the parasite. A precursor protein of 38 kDa was detected in amastigotes and stationary phase promastigotes with antisera specific to the LmCPa pro‐region, but was barely detectable in early log‐phase promastigotes. Anti‐central domain antisera recognized the 38 kDa precursor and 24 and 27 kDa proteins. The major CPs ofL. mexicanaamastigotes, previously designated types A, B and C, were not detected with the antisera, suggesting that the gene codes for a previously uncharacterized CP inL. mexicana.The 24 kDa protein detected by the antiserum has no activity towards gelatin but apparently hydrolyses the peptide substrate BzPhe‐ValArgAMC. The relative levels of the 24 and 27 kDa proteins vary between the different life‐cycle stages. The results indicate that expression of this CP is regulated at both th

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01365.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryTransmission of unmodified plasmid Collb‐P9 by bacterial conjugation is markedly resistant to restriction compared with transfer by transformation. One process allowing evasion of type I and II restriction systems involves conjugative transfer of multiple copies of the plasmid. A more specialized evasion mechanism requires the Ard (alleviation of restriction of DNA) system encoded by Collb. Theardgene is transferred early in conjugation and specifically alleviates DNA restriction by all known families of type I enzyme, includingEcoK. Collb has no effect onEcoKmodification but this activity is impaired by multicopy recombinant plasmids supporting overexpression ofard.Genetic evidence shows that Ard protects Collb fromEcoK restriction following conjugative transfer and that this protection requires expression of the gene on the immigrant plasmid. It is proposed that carriage ofardfacilitates transfer of Collb between its natural enterobacterial hosts and that the route of DNA entry is important to the restriction‐evasion mechan

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01366.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryCitrate is fermented byKlebsiella pneumoniaeto 2 acetate, 0.5 formate and 1.2 CO2. The formation of‐100 mV. NADH formation was completely abolished in the presence of oxygen or after addition of hydroxyquinoline‐N‐oxide, a specific inhibitor of the Na+‐translocating NADH:ubiqurnone oxidoreductase. The increase of endogenous NADH was dependent on the δpNa+applied to the cells. Inverted membrane vesicles ofK. pneumoniaecatalysed the reduction of NAD+to NADH with formate as electron donor after application of delta;μTNa+of about 120 mV consisting of δpNa+of 60 mV and ΔΨ of the same magnitude. Neither the δpNa+nor the ΔΨ of this size alone was sufficient to drive the endergonic reaction. Strictly anaerobic conditions were required for NADH formation and hydroxyquinoline‐N‐oxide completely inactivated the reaction. It is suggested that NADH formation by reversed δμTNa+‐coupled electron transfer in these cells is an essential requirement for the synthesis

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb01367.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY