摘要:

SummaryPeptide chain termination occurs when a stop codon is decoded by a release factor. InEscherichia colitwo codon‐specific release factors (RF1 and RF2) direct the termination of protein synthesis, while in eukaryotes a single factor is required. TheE. colifactors have been purified and their genes isolated. A combination of protein and DNA sequence data reveal that the RFs are structurally similar and that RF2 is encoded in two reading frames. Frame‐shifting from one reading frame to the next occurs at a rate of 50%, is regulated by the RF2‐specific stop codon UGA, and involves the direct interaction of the RF2 mRNA with the 3’end of the 16S rRNA. The RF genes are located in two separate operons, with the RF1 gene located at 26.7 min and the RF2 gene at 62.3 min on the chromosome map. Ribosomal binding studies place the RF‐binding region at the interface between the ribosomal subunits. A possible mechanism of stop‐codon recognition

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00658.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryGroup I introns are present in at least three bacteriophage T4 genes:td, nrdBandsunY.The transcription products of these three genes have similar intron consensus regions and secondary structures, which render them capable of guanosine‐mediatedin vitroautocatalytic splicing reactions. Moreover, it has been shown that the 245‐amino‐acid protein encoded in thetdintron expresses an endonuclease that cleaves near the joining site for the two exons in the intron‐deleted thymidylate synthase gene. The intron‐containingtdgene is resistant to the enzyme. As in the case of other group I intron‐containing genes that have been described in eukaryotes, which also encode site‐specific endonucleases, thetdintron is highly mobile and can insert into the intronlesstdgene by a process initiated by endonuclease cleavage near the insertion site. Whether intron transposition reactions have any physiological significance to the phage, or represent an early imprint on the evolution of introns, remains to

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00659.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryRecent studies have identified two sub‐families of highly conserved polypeptides in a wide variety of organisms concerned with the transport of many different compounds, specific for each transport protein. Both famines, represented by HisP and HlyB, respectively, have in common a highly conserved, approximately 25kD domain, containing an ATP‐binding site. The HisP sub‐family essentially consists of cytoplasmic proteins which couple energy to theimportof small substrates through cytoplasmic membrane permeases in Gram‐negative bacteria. The HlyB (P‐glycoprotein) sub‐family, on the other hand, contains a second large domain which apparently acts as the transmembrane translocator itself, which in most cases drives thesecretionof a variety of compounds. These membrane domains share a number of structural features which also serve to distinguish these proteins as a closely related group. Nevertheless, the compounds secreted by the HlyB sub‐family Include large polypeptides, polysaccharides and a variety of anti‐tumour drugs. We describe here the properties of each of these remarkable proteins and we speculate on their possible mech

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00660.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryWe present evidence that DNA from diverse prokaryotic and eukaryotic sources gives rise to low‐level fusion expression inEscherichia colipromoter‐probe vectors. This expression may be as high as 10% of theE coli lac UV5promoter. Although expression does not correlate with the presence of obviousE. colipromoter‐like sequences, it is blocked by transcriptional terminators. Furthermore, transcription across the fusion junction is detected at levels that correlate with fusion expression. We suggest that this Mow‐level transcription'(LLT) results from infrequent initiation by RNA polymerase at random sites and/or weak promoters. We propose that LLT has biological significance. In some instances, it may provide an advantageous basal level of gene expression, and we suggest that this may be true for theE. coli lac Ygene. In other instances, LLT may be detrimental, in which case it may be blocked by mechanisms such as RNA secondary structure or transcriptional polarity. We present evidence to show that activation of the IS 10 transposase gene by LLT is blocked at the translationa

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00661.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryThe location of the structural gene for aggregation substance on the sex pheromone plasmid pAD1 ofEnterococcus faecaliswas determined using an oligonucleotide deduced from the N‐terminal amino acid sequence of the purified protein. The nucleotide sequence was determined for the corresponding region and two open reading frames (ORFs) could be identified. ORF1 codes for a small (Mr13160) acidic protein of unknown function. The gene for aggregation substance (namedasa1was found to code for a protein of 1296 amino acids (Mr142248). The protein has a signal peptide of 43 amino acids (the resulting (Mrfor mature aggregation substance is 137429) and contains in its C‐terminal region a proline‐rich sequence, previously characterized as being involved in cell wall association, which is followed by a membrane anchor. The membrane anchor showed significant similarity to that of other Gram‐positive organisms, but no other similarities to surface proteins from Gram‐positive bacteria were found. In particular, no repeats on the DNA or protein level could be detected for pAD1‐specific aggregation substance. The protein contains the amino acid motifs Arg‐Gly‐Asp‐Ser and Arg‐Gly‐Asp‐Val (once each), which, it is proposed, play a crucial role in adhere

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00662.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryYersiniaandSalmonellaharbour plasmids that encode traits important for virulence, enabling both pathogenic genera to survive and grow in cells of the reticulo‐endothelial organs during systemic infections. We have detected DNA homology between theSalmonella dublinvirulence plasmid pSDL2 and the plasmids of the pathogenicYersiniaspeciespestis, pseudotuberculosis, andenterocolitica.Three regions of pSDL2 were found to share homology with the virulence plasmid pIB1 ofYersinia pseudotuberculosis.Two separate hybridizing segments mapped within the previously characterized 6.4 kbvirregion of pSDL2 in theSal1B fragment. The third homologous region involved the regions of plB1, which hybridized to theSal1C2 fragment of pSDL2. The virulence plasmid pCD1 fromY. pestisshowed similar homology with the three regions of pSDL2. Homologies to thevirandSal1C2 regions of pSDL2 were also found on plasmids fromYersinia enterocoliticaserotypes 0:9, 0:3 and 0:5, 27. The discovery of separate homologous regions on the virulence plasmids ofSalmonellaandYersiniasuggests a distant evolutionary relationshi

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00663.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryNon‐β‐lactamase‐ producing, penicillin‐resistant strains ofNeisseria gonorrhoeae(CMRNG strains) produce altered forms of penicillin‐binding protein 2 (PBP2) that have decreased affinity for penicillin. A feature of PBP2 from all CMRNG strains is the presence of an additional residue (Asp‐345A) that is absent from PBP2 of penicillin‐sensitive strains. The role of the additional aspartic acid residue in the decreased affinity of PBP2 is unclear as PBP2 of all previously examined CMRNG strains possess several other amino acid sequence alterations, in addition to the insertion of Asp‐345A, compared to PBP2 of penicillin‐sensitive strains. Site‐directed mutagenesis has been used to insert the Asp‐345A codon into thepenAgene from a penicillin‐sensitive gonococcus. The resultingpenAgene expressed an altered form of PBP2 that had a decreased affinity for benzylpenicillin and was able to transform a pencillin‐sensitive strain ofN. gonorrhoeaeto an increased level of resistance to benzylpenicillin. Insertion of amino acids other than aspartic acid did not produce forms of PBP2 that provided increased resistance to penicillin. Removal of the Asp‐345A codon from thepenAgene of a CMRNG strain reduced its ability to transform a penicillin‐sensitive strain to an increased level of penicillin resistance. The reduction in the affinity of PBP2 in CMRNG strains is therefore largely, although not exclusively, due to the insertion of Asp‐345A. Clinical isolates that produce altered forms of PBP2 that differ from that of penicillin‐sensitive strains only in the insertio

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00664.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryIn a strain ofRhizobium leguminosarumbiovarphaseoli, three copies of the regulatory nodulation genenodDwere identified on the Sym plasmid and sequenced. Two were closely linked to each other and the third was near, but not adjacent, to thenodABCgenes. Each of thesenodDgenes could correct the Nod defect of anodDmutant strain ofR. leguminosarumbiovarviciaeon peas. A truncated form ofnodD2could also correct this mutant, indicating that theC‐terminus of NodD2 is not needed for inducing activity. Upstream ofnodD1and in the same operon is a newly described gene,nolE, whose product appears to be exported into the periplasm. Close tonodD2is another gene,nolP, with no known counterpart in other rhizobia. BothnolPandnolE‐nodD1are preceded by ‘nod‐box’ sequences and, in the former case, there appear to be two tandemly repeated nod‐box sequences. Mutations in each of thenodDgenes and in thenolEandnolPgenes did not abolish nodulation or nitrogen fixati

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00665.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryThe threenodDgenes of a strain ofRhizobium leguminosarumbiovarphaseoliwere cloned to study their effects on transcription of themselves and of thenodCgenes of biovarsphaseoliandviciae.Efficient transcription ofnodD1requirednodD1and was enhanced by exposure of the cells to bean exudate consistent with the presence of a nod‐box preceding thenolE‐nodD1operon. Transcription ofnodD2andnodDZwas constitutive.nodCofR. leguminosarumbiovarphaseoliwas activated by each of thenodDgenes of that biovar in the absence of inducers but expression was enhanced in cells grown with bean exudate or the flavonoids genistein or naringenin. A mutant ofnodD2, tacking 60bp at its 3’end, activatednodCin the presence of inducer, but was defective in regulating certain of thenodDgenes. ThenodCgene ofR. leguminosarumbiovarviciaeresponded differently to the variousnodDgenes ofR. leguminosarumbiovarphaseolithan did thenodCof the latter b

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00666.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SummaryThe overexpression of a subgene encoding a hybrid lipoyl domain of the dihydrolipoamide acetyltransferase component of the pyruvate dehydrogenase complex ofEscherichia colihas previously bee shown to result in the formation of lipoylated an unlipoylated products. Overexpression of the same subgene in a lipoic acid biosynthesis mutant growing under lipoate‐deficient conditions has now bee shown to produce domains modified by octanoylation as well as unmodified domains. It was concluded from the mass of a lipoyl‐binding‐site peptide that the modification involves N6‐octanoylation of the lysin residue (Lys244) that is normally lipoylated, and this was confirmed by the trypsin‐insensitivity of the corresponding Lys244‐Ala245 bond, and the absence c modification in a mutant domain in which Lys244 is replaced by Gin. This novel protein modification raise interesting questions concerning the pathway of lipoic acid biosynthesis and the mechanism of enzyme

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1990.tb00667.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY