摘要:

SummaryDictyostelium dfscoideumsynthesizes a 23000 Mrprotein, p23dd‐ras, closely related to the mammalian oncogene‐encoded protein p21ras. To investigate the subcellular localization of P23dd‐ras, conditions were optimized to reduce protein degradation following cell breakage. Subcellular fractionation ofD. discoideumshowed that p23dd‐raswas associated predominantly with the membrane fraction during both vegetative growth and differentiation, in the absence of suitable protease inhibitors considerable amounts of a truncated form of p23dd‐raswere recovered in the cytosol fraction, suggesting that intact p23dd‐rasis attached to the membrane by a short terminal peptide sequence. Radio‐isotope labelilng ofD. discoideumwith myristic acid or palmitic acid in the presence of excess un‐labelled acetate resulted in radio‐isotope incorporation into a select group of proteins including p23dd‐ras. No acyl label appeared in the truncated cytoplasmic form of p23dd‐raswhen ceil breakage was performed In the absence of suitable protease inhibitors, indicating that the acyl group is associated with the short terminal peptide that is cleaved. These data suggest that p23dd‐raslike its mammailan counterpart, is acylated and associated with the plasma membrane. There was no evidence during a 30‐minute pulse of methionine for a cytoplasmic precursor to the membrane‐bound p23dd‐rassuggesting that the turnover of the presumptive precursor must be much more rapid inD. discoideumthan for

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1987.tb01941.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SummaryThe increasing number of penicillin‐resistant clinical strains ofStrepfococcus pneumoniaehas raised questions about the mechanism involved. We have isolated a large number of independent, spontaneous laboratory mutants with increasing resistance against either piperacillin or cefotaxime. Both classes of mutants showed a different pathway of penicillin‐binding protein (PBP) alterations, and within each group of mutants the individual PBPs appeared to have changed at different resistance levels and in different sequences. The mutations led to decreased β‐lactam affinity and possibly to a reduction in the amount of protein present in the cell, but differences in apparent molecular weight, like those reported in low‐ and high‐level resistant pathogenic strains, were not found. Some mutants showed a high degree of cross‐resistance to a variety of pencillins and cephaiosporins independently of the acquired PBP alterations, indicating that different genotypes can be responsible for the same phenotypic expression o

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1987.tb01942.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SummaryThe halophilic archaebacterium,Halobacterium halobium, displays spontaneous and revertible genetic variability for the gas vesicle phenotype (Vac) at frequencies as high as 0.5 to 5%. To investigate the mechanism of these high‐frequency mutations, we have cloned a gas vesicle protein gene (gvpA) from the Vac+wild‐typeH. halobiumstrain, NRC‐1, and determined its nucleotide sequence, transcription start site, and genomic location. The gene sequence predicts that the gas vesicle protein has a molecular weight of 9156 and is relatively hydrophobic except for a hydrophilic C‐terminal region. Northern hybridization analysis shows that the gene is transcribed into a 350‐nucleotide mRNA, and primer extension analysis indicates that transcription begins 20 nucleotides upstream of the ATG start codon. Southern hybridization analysis shows that the gene is encoded by a largeH. halobiumplasmid. We discuss potential mechanisms for genetic variability of the Vac phenotype and identify sequences in thegvpApromoter region which may function as signals for transcription inH.

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1987.tb01943.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SummaryClostridium perfringensstrain CPN50 harbours a 10.2 kb plasmid known as plP404 which, in addition to a set of UV‐inducible genes involved in bacteriocin production, carries res, a gene probably encoding a site‐specific recombinase. The RES protein is highly homologous to the resolvases of transposons from both Gram‐negative and Gram‐positive bacteria as well as enzymes involved in site‐specific DNA inversion. A likely role for the RES protein would be to stabilize plP404 by reducing the number of plasmid multimers resulting from homologous recombination. A putative resolution site for RES action was found overlapping therespromoter. Phylogenetic analysis of the primary structures of ten site‐specific recombinases suggested a common descent and showed the RES protein to be closest to the resolvase encoded by Tn917 fromStrepfococc

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1987.tb01944.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SummaryThe nature of pili synthesized byPseudomonas aeruginosawhen plasmid‐borne genes of homologous pilins fromBacteroides nodosusare Introduced as thermoregulated expression systems has been ascertained. Expression ofB. nodosuspili inhibited the production of indigenousP. aeruginosa pili, and an organism harbouring pilin genes from two strains ofB. nodosusproduced two seroiogically distinct populations of pili on each cell. Simultaneous production of both Indigenous and foreign pili was achieved by partial induction of expression. Homogeneity in pilus structure suggests either that there is an exclusive specificity of Interaction between identical pilin subunits in pilus assembly, or that each pilus is produced from the translation products of a single messenger RNA molecule, with translation and pilus assembly closely couple

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1987.tb01945.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SummarySoft rotErwiniaspecies secrete a range of enzymes into the extracellular environment. Therefore, the genetically amenableErwiniasystem is a useful model for the study of protein secretion by Gram‐negative bacteria. We have used a λ‐sensitive derivative ofErwinia carotovorasubspeciescarotovora(Ecc) and the transposonTnphoA, to isolate a range of extracellular enzyme mutants. The use ofTnphoAprovides an enrichment for extracellular enzyme mutants over other transposon‐based systems. In these mutants, the alkaline phosphatase activity of the hybrid protein Is found in the periplasm, and is under the control of the Ecc promoters. Three TnphoA‐induced extracellular enzyme mutants were studied in detail. One proved to be an enzyme structural gene mutant, whilst the other two appeared to be secretory

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1987.tb01946.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY