摘要:

SummarySecondary metabolites are proposed to have played important roles in the evolution of the reactions of living forms on earth, in effecting and modulating reactions during biochemical evolution by chemical and structural interaction with ‘receptor’ sites in primitive macromolecular templates. For example, in the evolution of the translation system, as the polymerizing reactions became more complex and proteins became involved, the low molecular‐weight effectors were functionally replaced by polypeptides, but retained their ability to interact with receptor sites in nucleic acids and proteins. Many of these low molecular‐weight effectors now play a different role, that of antagonists, by interacting with the original receptor sites in contemporary activity as anti

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00701.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryPost‐transcriptional control mechanisms assume special significance in polycistronic operons. Differential gene expression in theatpoperon ofEscherichia coliis primarily attributable to translational control and, to a lesser extent, to control of mRNA stability. At the same time, the polycistronic environment influences, to varying degrees, the relative importance of the different types of post‐transcriptional control. The present article briefly reviews more recent results obtained through studies of theatpoperon. Investigations of the pathway and kinetics of mRNA decay have yielded new information about the role of degradative mechanisms in the overall scheme of control. Moreover, translational coupling has been shown to feature as a major form of interaction between theatpgenes. The relevance of these and other data is discussed in the wider context of the post‐transcriptional control mechanisms generally available toE.

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00702.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryTetracycline resistance in the Enterobacteriaceae is mediated by a number of genetically related, usually plasmid‐borne, determinants which specify an efflux system involving an inner membrane protein, Tet. Attempts to overproduce the Tn10(Class B)‐encoded Tet inEscherichia coliby cloning the structural genetetdownstream of the λPLpromoter under regulation by temperature‐sensitive λ repressorc1857 were unsuccessful; induction at 42°C resulted in filamentous, non‐viable cells containing little detectable overproduction of the protein. However, cells containingtetfused tolacZwere resistant to tetracycline at 30°C and synthesized modest amounts of a large fusion protein when induced at 42°C. Fusion of theN‐terminal half or the first 38 amino adds oftettolacZdid lead to increased production of fusion proteins. Fusions could be purified by size or by LacZ immunoaffinity or substrate‐affinity chromatography. In the latter method, selected detergents were required to counteract nonspecific binding of Tet to the adsorbant. Amino acid sequencing of theN‐terminus of Tet–LacZ fusion proteins indicated that most molecules were blocked at this terminus. The sequence of an unblocked subpopulation was consistent with that expected from the nucleotide sequence. A collagen peptide linker, genetically placed betweentetandlacZ, allowed recovery of purified Tet protein after collagenase treatment of the pur

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00703.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryThe influence of theKlebsiella pneumoniae nifLgene product upon the interaction of the transcriptional activator protein NifA with thenifHpromoter has been examined usingin vivodimethylsulphate ‘footprinting’. Binding of NifA to the upstream activator sequence (UAS) of thenifHpromoter in the presence of the NifL protein was observed under nitrogen‐limiting growth conditions. Growth in the presence of NH+4or addition of NH+4to nitrogen‐limited cells diminished the interaction of NifA with the UAS when NifL was present. Repression ofniftranscription by NifL may therefore involve an interaction between NifL and NifA which reduces the affinity of NifA for

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00704.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryThe TraT protein is a surface‐exposed lipoprotein, specified by plasmids of the IncF group, that mediates serum resistance and surface exclusion. The structure and function of the TraT protein determined by plasmid R6‐5 was probed by genetic insertion of a foreign antigenic determinant, the C3 epitope of polio virus, at residues 61, 125, 180, 200 or 216 of the protein. The chimaeric proteins were transported to the outer membrane and, in three cases, immunoassays with an anti‐C3 monoclonal antibody indicated that the C3 epitope was exposed on the cell surface. Three of the hybrids, with insertions at residues 125, 180 and 200, assembled into the trypsin‐resistant oligomeric form characteristic of the wild‐type protein, which suggested that these regions are not involved in TraT subunit:subunit interactions. Additionally, the hybrid protein carrying the C3 epitope at position 180 functioned in a genetic suppression assay and retained partial surface‐exclusion activity. Thus, its localization, folding and organization does not appear to be grossly altered from that of the wild‐type protein. Applications of the protein for the transport of foreign antigenic determinants to the cell surface

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00705.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryHuman lysosomal cathepsin G (cat G) appears to be an important mediator of non‐oxidative killing ofNeisseria gonorrhoeaeingested by human polymorpho‐nuclear leucocytes (PMNLs). Nearly isogenic strains of gonococci having variations in the structure of penicillin‐binding protein 2 (PBP2) also exhibit different levels of susceptibility to the lethal action of cat Gin vitro.Accordingly, we examined the relationship between gonococcal susceptibility to cat G and PBP2 structure. The results of this study suggest that cat G has the capacity to interact with PBP2, as evidenced by its ability to inhibit binding of [3H]‐benzylpenicillin to PBP2. We also found that changes in the amino acid sequence within the transpeptidase domain of PBP2, because of certainpenAmutations, modulated such interactions. We propose that PBP2 is an intracellular target for cat G and that levels of gonococcal susceptibility to cat G may be related to PBP2 structure and/or intracellular avail

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00706.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryThe maintenance of late gene expression by 3′ 5′ cyclic AMP was re‐examined using several newly isolated cell‐type‐specific genes. Expression of all the prespore‐enriched genes ceased immediately upon disaggregation of developing cells and pre‐existing mRNA was rapidly degraded. For most genes, cAMP had little or no effect either alone or in combination with conditioned medium factors. The expression of the non‐cell‐type‐specific genes 7E and 2C also ceased upon cell disaggregation but cAMP triggered a full re‐induction of expression although the timing of the response differed markedly between these two genes. In contrast to earlier interpretations, these data argue that for none of these late prespore genes is cAMP alone sufficient for the maintenance of expression. The responses of the two prestalk mRNAs examined were gene‐specific. Prestalk 5D mRNA decayed slowly upon disaggregation and was partially stabilized by cAMP whereas prestalk 5G mRNA increased upon disaggregation an

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00707.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryResistance to normal human serum (NHS) killing inNeisseria gonorrhoeaehas been associated with particular types of Protein I (PI) and lipopolysaccharide (LPS), but many exceptions exist, and the role of these structures in determining serum reactivities remains controversial. In reality, the response of the gonococcus to NHS is probably governed by several parameters involving a number of outer‐membrane (OM) components. We surveyed the serum reactivities of 14 strains ofN. gonorrhoeaeand characterized each of their major OM components. The strains presented a spectrum of sensitivity to pooled NHS. As assessed by sodium dodecyl sulphate–polyacrylamide gel electrophoresis, immunoblotting, and peptide mapping, the strains were also quite heterogeneous in terms of PI, H.8 antigen, and LPS type, and the presence of the 2‐1‐L8 epitope. Five of the strains had identical PIAs in varying LPS and H.8 backgrounds, and four had Identical PIBs in varying LPS and H.8 backgrounds. As assessed by electrophoretic migration and monoclonal antibody binding. Protein III and the 44000 Dalton protein were identical in these strains. We found no association between PI subclass and serum sensitivity, while H.8 and LPS variation appeared to be related to bactericidal responses. The diversity and close interaction of gonococcal components in the OM are undoubtedly involved in differential abilities to survive NHS

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00708.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryTheMycoplasma pneumoniae tufgene, encoding the elongation factor protein Tu, was cloned and sequenced. The nucleotide sequence of the mycoplasmal gene showed about 60% homology to the sequences oftufgenes of other prokaryotes, yeast mitochondria andEuglena gracilischloroplasts, and about 75% similarity was found when comparing the deduced amino acid sequences of the various Tu proteins. The relatively low G+C content (40%) of theM. pneumoniaeDNA was reflected in a low G+C content (44.6%) of thetufgene, and in a preferential use of adenine and uracil at the third position of codons, yet codon usage analysis revealed the presence of almost all of the codons of the genetic code in the mycoplasmal gene. Southern blot hybridization of digested DNAs of 11 Mollicutes species with the entireM. pneumoniae tuf geneand with its 5′ part suggested the presence of one copy only of this gene in the representative species of the Mollicutes. In this respect, the Mollicutes resemble Gram‐positive bacteria and differ from the Gram‐negative bacteria, which carry two copies of thetu

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00709.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryThe relationship between type 1 pilus structure and the mannose‐sensitive adhesin was investigated by analysing the properties of an 11.2 kb fragment of DNA derived from the chromosomalpilregion of a type 1 piliated uropathogenic strain ofEscherichia coli.The recombinant plasmids pHA9 and pSJH9, containing the cloned fragment, conferred a mannose‐sensitive haemagglutination (MSHA)‐positive but non‐piliated phenotype on recipient cells of ORN104. Most of the DNA sequences homologous to thepilAandhypgenes were not present in the 11.2kb insert, and the genetic information necessary for MSHA in the absence of piliation spanned a 6.5 kb region of the cloned fragment. The polypeptides expressed by pSJH9 were examined in minicells and Tn1000insertions in three genes encoding proteins of molecular weights 90 kD, 29 kD and 17kD abolished the MSHA ph

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00710.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY