ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb00830.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryDNA helicases are ubiquitous enzymes that catalyse the unwinding of duplex DNA during replication, recombination and repair. These enzymes have been studied extensively; however, the specific details of how any helicase unwinds duplex DNA are unknown. Although it is clear that not all helicases unwind duplex DNA in an identical way, many helicases possess similar properties, which are thus likely to be of general importance to their mechanism of action. For example, since helicases appear generally to be oligomeric enzymes, the hypothesis is presented in this review that the functionally active forms of DNA helicases are oligomeric. The oligomeric nature of helicases provides them with multiple DNA‐binding sites, allowing the transient formation of ternary structures, such that at an unwinding fork, the helicase can bind either single‐stranded and duplex DNA simultaneously or two strands of single‐stranded DNA. Modulation of the relative affinities of these binding sites for single‐stranded versus duplex DNA through ATP binding and hydrolysis would then provide the basis for a cycling mechanism for processive unwinding of DNA by helicases. The properties of theEscherichia coliDNA helicases are reviewed and possible mechanisms by which helicases might unwind duplex DNA are discussed in view of their oligomeric structures, with emphasis on theE. coliRep, RecBCD and phage T7 gene4he

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb00831.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryUnderstanding the mechanism of glucose repression in yeast has proved to be a difficult and challenging problem. A multitude of genes in different pathways are repressed by glucose at the level of transcription. TheSUC2gene, which encodes invertase, is an excellent reporter gene for glucose repression, since its expression is controlled exclusively by this pathway. Genetic analysis has identified numerous regulatory mutations which can either prevent derepression ofSUC2or render its expression insensitive to glucose repression. These mutations allow us to sketch the outlines of a pathway for general glucose repression, which has several key elements: hexo‐kinase PII, encoded byHXK2, which seems to play a role in the sensing of glucose levels; the protein kinase encoded bySNF1, whose activity is required for derepression of many glucose‐repressible genes; and the MIG1 repressor protein, which binds to the upstream regions ofSUC2and other glucose‐repressible genes. Repression by MIG1 requires the activity of the CYC8 and TUP1 proteins. Glucose repression of other sets of genes seems to be controlled by the general glucose repression pathway acting in concert with other mechanisms. In the cases of theGALgenes and possiblyCYC1, regulation is mediated by a cascade in which the general pathway represses expression of a positive transcriptional acti

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb00832.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryInEscherichia coli, chemotactic sensory transduction is believed to involve phosphoryl transfer for excitation, and changes in receptor methylation for adaptation. InBacillus subtilis, changes in degree of receptor methylation do not bring about adaptation. Novel methylation reactions are believed to be involved in excitation inB. subtillis.The main chemotaxis proteins ofE. coli—CheA, CheB, CheR, CheW and CheY—are present inB. subtilisbut play somewhat different roles in the two organisms. Several unique chemotaxis proteins are also present inB. subtilis.Some of the properties ofB. subtilischemotaxis are also seen inHalobacterium halobium, suggesting that there may be a similar underlying mechanism that predates the evolutionary separation of the bacteria from the archaea and euca

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb00833.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryIt is argued that organisms have evolved the ability to biosynthesize secondary metabolites (natural products) because of the selectional advantages they obtain as a result of the functions of the compounds. The clustering together of antibiotic biosynthesis, regulation, and resistance genes implies that these genes have been selected as a group and that the antibiotics function in antagonistic capacities in nature. Pleiotropic switching, the simultaneous expression of sporulation and antibiotic biosynthesis genes, is interpreted in terms of the defence roles of antibiotics. We suggest a general mechanism for the evolution of secondary metabolite biosynthesis pathways, and argue against the hypothesis that modern antibiotics had prebiotic effector functions, on the basis that it does not account for modern bio‐synthetic pathway

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb00834.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryThe replication region of the plasmid pHT1030 ofBacillus thuringiensiswas previously mapped to a 2.9 kb DNA fragment. The DNA sequence was analysed and it was shown that the minimal replicon resides within a 1 kb fragment of DNA carrying no potential protein coding sequence. Moreover, no production of single‐stranded DNA intermediates was detected in the plasmid‐containing cells. pHT1030 therefore belongs to a class of replicons not previously described in Gram‐positive bacteria. Examination of the segregational stability of deletion derivatives of pHT1030 in bacilli defined two stability regions. One is located within the minimal replicon of pHT1030, whereas the second (spbA) is not required for replication.spbAencodes a 15 kDa protein and ensures the segregational stability of the plasmid. This effect ofspbAis particularly highlighted in sporulation. The absence of thespbAlocus gives rise to plasmid‐free spores at high frequency, whereas thespbA+plasmids are stably maintained. The stability of the plasmids during sporulation seems to be correlated with an unequal division of the cell by the sporulation

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb00835.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryThe oligopeptide permease ofSalmonella typhimuriumis a periplasmic binding protein‐dependent transport system. Five gene products, OppABCDF, are required for the functioning of this transporter, two of which (OppB and OppC) are highly hydrophobic, integral membrane proteins and are responsible for mediating passage of peptides across the cytoplasmic membrane. OppB and OppC are each predicted, from their sequences, to span the membrane many times. In this paper we describe experimental evidence confirming these predictions using a combination of biochemical, immunological and genetic procedures. Each of these two proteins is shown to span the membrane six times, with theN‐ andC‐termini both being located at the cytoplasmic face of the membrane. Opp is apparently a typical member of the ABC (ATP‐bindingcassette) superfamily of transporters. These findings, therefore, have general implications for the organization and function of other ABC transporters, including the human multidrug resistance protein and the product of the cystic fibros

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb00836.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryThePseudomonas aeruginosaexopolysaccharide alginate is an important virulence factor in chronic pulmonary infections of cystic fibrosis patients. We determined the nucleotide sequence of the gene,algB, which regulates the level of exopolysaccharide produced by mucoidP. aeruginosa.The predicted amino acid sequence of AlgB revealed a high degree of similarity to the regulatory proteins in the NtrC subclass of ‘two‐component regulatory systems’. AlgB expression inEscherichia coliminicells showed a molecular weight of ˜ 50 000 Da, comparable to that of the inferred amino acid sequence (49 318 Da). We show thatalgBis transcriptionally active in mucoid strains ofP. aeruginosaand regulates the expression of the alginate biosynthetic gene,algD, thereby resulting in increased expression of alginate in mucoidP. aeru

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb00837.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryThenit‐4genes of three conventionalNeurospora crassamutations and of the closely related species,Neurospora intermedia, have been isolated by amplifying the genomic DNA with the polymerase chain reaction. Nucleotide sequencing has revealed that the threenit‐4mutants, alleles 15,1214, and 2994, are the result of a missense mutation, a nonsense mutation and a frameshift mutation, respectively. The nucleotide sequence of the NIT4 protein coding region of anit‐4mutant (allele 2994) and ofN. intermediahave been determined and compared with that of wild‐typeN. crassa.The molecular characteristics confirm that the mutated gene of 2994 originated fromN. intermediaand was introgressed intoN. crassa.The polyglutamine domains of theN. crassawild type, the 2994 mutant, orN. intermediacannot replace an upstream glutamine‐rich domain which is essential fornit

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb00838.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SummaryA library of random yeast genomic DNA:lacZfusions has been constructed using an episomal yeast‐Escherichia colishuttle vector (pCS1). Plasmid pCS1 requires insertion of a promoter and an inframe ATG codon upstream of its resident truncatedlacZgene to regulate expression in yeast. Yeast genomic DNA fragments of 4–6 kb were generated by partial digestion withSau3Aand ligated into the uniqueBamHIsite of plasmid pCS1 to generate a library of 5 × 104individualE. colitransformants. This library was screened to identify promoter‐lacZfusions that were expressed uniquely during sporulation. Of 342 yeast transformants that exhibited β‐galactosidase activity, two were found to express thelacZgene in a sporulation‐specific manner.This paper presents the characterization of two genomic yeast DNA fragments containing promoters that controllacZexpression during the sporulation process. Expression from the promoter present in plasmid pJC18 occurred from 11–21 hours into the sporulation process, while the promoter in plasmid pJC217 was active from 4–14 hours. Staining of nuclear DNA to correlate nuclear morphology with timing of gene expression showed when each of these promoters was active in terms of the morphological stages

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1992.tb00839.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY