摘要:

SummaryThree components involved in catabolite repression (CR) of gene expression inBacillushave been identified. Thecis‐acting catabolite responsive element (CRE), which is present in many genes encoding carbon catabolic enzymes in various species of the Gram‐positive bacteria, mediates CR of several genes inBacillus subtilis, Bacillus megaterium, andStaphylococcus xylosus.CR of most genes regulated via CRE is also affected by thetrans‐acting factors CcpA and HPr. Similarities between CcpA and Lac andGalrepressors suggest binding of CcpA to CRE. HPr, a component of the phosphoenol pyruvate:sugar phosphotransferase system, undergoes regulatory phosphorylation at a serine residue by a fcuctose‐1,6‐diphosphate‐activated kinase. A mutant of HPr, which is not phosphorylatable at this position because of an exchange of serine to alanine, lacks CR of several catabolic activities. This mutant phenotype is similar to the one exhibited by accpAmutant. Direct protein‐protein interaction between CcpA and HPr(Ser‐P) was recently demonstrated and constitutes a link between metabolic

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.tb02252.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryAlkaliphilicBacillusspecies provide experimental opportunities for examination of physiological processes under conditions in which the stress of the extreme environment brings issues of general biological importance into special focus. The alkaliphile, like many other cells, uses Na+/H+antiporters in pH regulation, but its array of these porters, and other ion‐flux pathways that energize and support their activity, result in an extraordinary capacity for pH homeostasis; this process nonetheless becomes the factor that limits growth at the upper edge of the pH range. Above pH 9.5, aerobic alkaliphiles maintain a cytoplasmic pH that is two or more units below the external pH. This chemiosmotically adverse δpH is bypassed by use of an electrochemical gradient of Na+rather than of protons to energize solute uptake and motility. By contrast, ATP synthesis occurs via completely proton‐coupled oxidative phosphorylation that proceeds just as well, or better, at pH10 and above as it does in the same bacteria growing at lower pH, without the adverse pH gradient. Various mechanisms that might explain this conundrum are described, and the current state of the evidence supporting them is summar

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.tb02253.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryMembers of a class of antisense RNAs are encoded by genes that are located at loci other than those of their target genes. Three examples of antisense RNA genes are discussed here.micFis found inEscherichia coliand other bacteria and functions to control outer membrane protein F levels in response to environmental stimuli.dicFis also found inE. coliand is involved in the regulation of cell division,lin‐4is found in the nematodeCaenorhabditis elegansand functions during larval development. Nucleotide sequences of at least two of these genes appear to be phylogenetically conserved. Thetrans‐encoded antisense RNAs are small RNAs which display only partial complementarity to their target RNAs. Models for RNA/RNA interactions have been proposed. It is possible that currently known unlinked antisense RNA genes are part of a larger class of heretofore undiscovered regulatory RNA genes. Possible ways of detecting other unlinked antisense RNA genes are discus

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.tb02254.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryMany parasitic DNA elements including prophages and plasmids synthesize proteins that kill the cell after infection by other phages, thereby blocking the multiplication of the infecting phages and their spread to other nearby cells. The only known function of these proteins is to exclude the infecting phage, and therefore to protect their hosts, and thereby the DNA elements themselves, against phage contagion. Many of these exclusions have been studied extensively and some have long been used in molecular genetics, but their molecular basis was unknown. The most famous of the phage exclusions are those caused by the Rex proteins of λ prophage. The Rex exclusions are still not completely understood, but recent evidence has begun to lead to more specific models for their action. One of the Rex proteins, RexA, may be activated by a DNA‐protein complex, perhaps a recombination or replication intermediate, produced after phage infection. In the activated state, RexA may activate RexB, which has been proposed to be a membrane ion channel that allows the passage of monovalent cations, destroying the cellular membrane potential, and killing the cell. We now understand two other phage exclusions at the molecular level which use strategies that are remarkably similar to each other. The parasitic DNA elements responsible for the exclusions both constitutively synthesize enzymes that are inactive as synthesized by the DNA element but are activated after phage infection by a short peptide determinant encoded by the infecting phage. In the activated state, the enzymes cleave evolutionarily conserved components of the translation apparatus, in one case EF‐Tu, and in the other case tRNALys. Translation is blocked and development of the phage is arrested. A myriad of different phage‐exclusion systems are known to exist and many of these may also be specific for highly conserved cellular components, furnishing generally useful enzymes for biochemical and biomedical re

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.tb02255.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryBacillus subtiliscontains at least three classes of heat‐shock genes regulated by different mechanisms. We are studying class I heat‐shock genes encoded by the operonsdnaKandgroE.These two operons are both expressed from a vegetative promoter, and their regulation involves a novel heat‐shock element designated CIRCE. Here we show that induction of both operons results from enhanced synthesis of mRNA and is independent ofde novoprotein synthesis. To answer the question of whetherdnaKis involved in the deregulation of the heat‐shock response as reported forEscherichia coli, two different insertion mutations were isolated within the tetracistronicdnaKoperon(orf39–grpE–dnaK–dnaJ).In one mutant a cat cassette was inserted at the beginning oforf39.Transcriptional analysis revealed that this mutation abolished expression of the whole operon. In contrast, the basal level ofgroEmRNA was significantly increased at 37°C, followed by a prolonged delay in the shut off after temperature upshift. These data point to a crucial role for theorf39gene in the regulation of class I heat‐shock genes. In the other mutant an internal 0.8 kbBglII fragment ofdnaKwas replaced by thecatcassette. In contrast toE. coli dnaKnull mutants, the twoB. subtilis dnaKoperon mutants could grow within a temperature range from 16–52°C. At temperatures above 52°C, they failed to form colonies on agar plates, started to filament, and lost motility. Furthermore, the induction profile of thegroEanddnaKoperons was not impaired in thednaK::catmutant. The expression of the flagellin gene is influenced on both the transcriptional and post‐transcriptional level. By Northern‐blot analysis we previously showed that expression of thednaKoperon resulted in two mRNA species of 4.9 and 2.6 kb. Our mutational analysis suggests the formation of the 2.6 kb transcript as a processing produ

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.tb02256.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryA segment ofThermotoga maritimastrain MSB8 chromosomal DNA was isolated which encodes an endo‐1,4‐β‐D‐xylanase, and the nucleotide sequence of the xylanase gene, designatedxynA, was determined. With a half‐life of about 40 min at 90°C at the optimal pH of 6.2, purified recombinant XynA is one of the most thermostable xylanases known. XynA is a 1059‐amino‐acid (˜120 kDa) modular enzyme composed of an N‐terminal signal peptide and five domains, in the order A1‐A2‐B‐C1‐C2. By comparison with other xylanases of family 10 of glycosyl hydrolases, the central ˜340‐amino‐acid part (domain B) of XynA represents the catalytic domain. TheNterminal ˜150‐amino‐acid repeated domains (A1‐A2) have no significant similarity to theC‐terminal ˜170‐amino‐acid repeated domains (C1‐C2). Cellulose‐binding studies with truncated XynA derivatives and hybrid proteins indicated that theC‐terminal repeated domains mediate the binding of XynA to microcrystalline cellulose and that C2 alone can also promote cellulose binding. C1 and C2 did not share amino acid sequence similarity with any other known cellulose‐binding domain (CBD) and thus are CBDS of a novel type. Structurally related protein segments which are probably also CBDs were found in other multi‐domain xylanolytic enzymes. Deletion of theN‐terminal repeated domains or of all the non‐catalytic domains resulted In substantially reduced tbermostability while a truncated xylanase derivative lacking theC‐terminal tandem repeat was as thermostable as the full‐length enzyme. It is argued that the multidomain organization of some enzymes may be one of the strategies adopted by ther

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.tb02257.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryWhen a liquid culture ofSerratiaspp. reaches the last part of the logarithmic phase of growth it induces the synthesis of several extracellular hydrolytic enzymes. In this communication we show that synthesis and secretion of the extracellular phospholipase is coupled to expression of flagella. Expression of flagella is demonstrated to follow a growth‐phase‐dependent pattern. Cloning, complementation studies and DNA‐sequencing analysis has identified a genetic region inSerratia liquefacienswhich exhibits extensive homology to theEscherichia coli flhDflagellar master operon. Interruption of the chromosomalflhDoperon inS. liquefaciensresults in non‐flagellated and phospholipase‐negative cells, but the synthesis of other exoenzymes is not affected. By placing theflhDoperon under the control of a foreign inducible promoter we have shown that increased transcription through theflhDoperon leads to induction of flagellar synthesis and phospholipase e

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.tb02258.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummarycomKis a positive autoregulatory gene occupying a central position in the competence‐signal‐transduction network. All regulatory routes identified in this network converge at the level ofcomKexpression. The ComK protein is required for the transcriptional induction ofcomKand the late competence genes, which specify morphogenetic and structural proteins necessary for construction of the DNA‐binding and uptake apparatus. In this report we demonstrate that ComK specifically binds to DNA fragments containing promoter and upstream sequences of the genes it affects(comC, comE, comF, comGandcomK) Using portions of the region upstream ofcomCwe show that the ComK‐binding sequences are essential for the expression of competence. Moreover, we demonstrate that the presence of ComK stimulates the expression ofcomF–lacZandcomG–lacZtranslational fusionsin vivoinEscherichia coliThese results indicate that the gene product ofcomKis identical to the previously inferred competence transcription f

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.tb02259.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryThe merozoite cap protein‐1 (MCP‐1) ofPlasmodium falciparumfollows the distribution of the moving Junction during invasion of erythrocytes. We have cloned the gene encoding this protein from a cDNA library using a monoclonal antibody. The protein lacks a signal sequence and has no predicted trans‐membrane domains; none of the antisera reacts with the surfaces of intact merozoites, indicating that the cap distribution is submembranous. MCP‐1 is divided into three domains. TheN‐terminal domain includes a 52‐amino‐acid region that is highly conserved in a large family of bacterial and eukaryotic proteins. Based on the known functions of two proteins of this family and the pattern of amino acid conservation, it is predicted that this domain may possess oxido‐reductase activity, since the active cysteine residue of this domain is invariant in all proteins of the family. The other two domains of MCP‐1 are not found in any other members of this protein family and may reflect the specific function of MCP‐1 in invasion. The middle domain is negatively charged and enriched in glutamate; theC‐terminal domain is positively charged and enriched in lysine. By virtue of its positive charge, theC‐terminal domain resembles domains in some cytoskeleton‐associated proteins and may mediate the interaction of MCP‐1 wit

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.tb02260.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummarySuccinate dehydrogenase (SDH) ofEscherichia coli, the sole membrane‐bound enzyme of the tricarboxylic acid cycle, participates in the aerobic electron‐transport pathway to generate energy via oxidative phosphorylation reactions. Previous studies have established that succinate dehydrogenase (SDiH) synthesis is elevated by aerobiosis and supressed during growth with glucose. To examine how thesdhCDABgenes that encode SDH are regulated by changes in the environment,sdh–lacZfusions were constructed and analysedin vivofollowing cell growth under a variety of alternative culture conditions. Expression ofsdh–lacZwas highest under aerobic conditions and was decreased 10‐foid in the absence of oxygen. ThefnrandarcAgene products are required for this oxygen control and each acts to represssdhC–lacZexpression. Expression ofsdh–lacZalso varied 10‐ to 14‐foid depending on the type of carbon substrate used or the medium richness. This control was shown to be independent of thecrpandfruRgene products, and indicates that some other regulatory element exists in the ceil to adjust SDH enzyme levels accordingly. Iron and haem availability affectedsdhC–lacZexpression by two‐ to threefold. Lastly, fold. Lastly,sdhC–lacZexpression was shown to vary with the cell growth rate during aerobic a

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.tb02261.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY