摘要:

SummaryThe members of the 10 kDa and 60 kDa heat‐shock chaperonin proteins (Hsp10 and Hsp60 or Cpn10 and Cpn60), which form an operon in bacteria, are present in all eubacteria and eukaryotic ceil organelles such as mitochondria and chloroplasts. In archaebacteria and eukaryotic cell cytosol, no close homologues of Hsp10 or Hsp60 have been identified. However, these species (or ceil compartments) contain the Tcp‐1 family of proteins (distant homologues of Hsp60). Phylogenetic analysis based on global alignments of Hsp60 and Hsp10 sequences presented here provide some evidence regarding the evolution of mitochondria from a member of the α‐subdivision of Gram‐negative bacteria and chloroplasts from cyanobacterial species, respectively. This inference is strengthened by the presence of sequence signatures that are uniquely shared between Hsp60 homologues from α‐purple bacteria and mitochondria on one hand, and the chloroplasts and cyanobacterial hsp60s on the other. Within the α‐purple subdivision, species such asRickettsiaandEhrlichia, which live intracellularly within eukaryotic cells, are indicated to be the closest relatives of mitochondrial Homologues, In the Hsp60 evolutionary tree, rooted using the Tcp‐1 homologue, the order of branching of the major groups was as follows: Gram‐positive bacteria — cyanobacteria and chloroplasts — chlamydiae and spirochaetes —β and γ‐Gram‐negative purple bacteria —α‐purple bacteria — mitochondria. A similar branching order was observed independently in the Hsp10 tree. Multiple Hsp60 homologues, when present in a group of species, were found to be clustered together in the trees, indicating that they evolved by independent gene‐duplication events. This review also considers in detail the evolutionary relationship between Hsp50 and Tcp‐1 families of proteins based on two different models (viz. archaebacterial and chimeric) for the origin of eukaryotic cell nucleus. Some predictions

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.tb02216.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryTransposable genetic elements have adopted two major strategies for their displacement from one site to another within and between genomes. One involves passage through an RNA intermediate prior to synthesis of a DNA copy while the other is limited uniquely to DNA intermediates. For both types of element, recombination reactions involved in integration are carried out by element‐specific enzymes. These are called transposases in the case of DNA elements and integrases in the case of the best‐characterized RNA elements, the retroviruses and retrotransposons. In spite of major differences between these two transposition strategies, one step in the process, that of insertion, appears to be chemically identical. Current evidence suggests that the similarities in integration mechanism are reflected in amino acid sequence similarities between the integrases and many transposases. These similarities are particularly marked in a region which is thought to form part of the active site, namely the DDE motif. In the light of these relationships, we attempt here to compare mechanistic aspects of retroviral integration with transposition of DNA elements and to summarize current understanding of the functional organization of integrases and transposa

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.tb02217.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryWe have carried out a functional analysis ofinvlandinvJ, twoSaimonella typhimuriumgenes required for this organism to gain access So cultured mammalian cells. These genes are located immediately downstream ofinvC, a previously identified gene also required for bacterial invasion. Non‐polar mutations in either of these genes renderedS. typhimuriumseverely defective for entry into cultured epithelial cells, although these mutations did not affect the ability of these organisms to attach to those cells. Nucleotide sequence analysis revealed that theinvlandinvJgenes encode proteins with molecular weights of 18077 and 36415, respectively. Polypeptides of similar sizes were observed when these genes were expressed in a bacteriophage T7 RNA polymerase‐based expression system. Comparison of the predicted sequences of Invl and InvJ with translated sequences in the existing databases indicated that these proteins are Identical to the previously identifiedS. typhimuriumSpaM and SpaN proteins. Further analysis of these sequences revealed regions of homology between Invl and theN‐terminus of lpaB ofShigellaspp. and between InvJ and EaeB of enteropathogenicEscherichia coli.Localization studies by immunoblot analysis indicated that InvJ is secreted to the culture supernatant, a surprising finding since this protein also lacks a typical signal sequence. Mutations ininvGandinyC, two members of theSalmonella invlocus, effectively prevented the transport of InvJ to the culture supernatant. Thus, InvJ is the first identified target of the protein secretion apparatus encoded in the inv locus and therefore a candidate to have effector functions related to bacterial

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.tb02218.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryTransfer of buddingCandida albicansyeast cells from the rich, complex medium YEPD to the defined tissue culture medium RPMl 1640 (RPMI) at 37°C and 5% CO2causes rapid onset of hyphal induction. Among the genes induced under these conditions are hyphal‐specific genes as well as genes expressed in response to changes in temperature, CO2and specific media components. A cDNA library constructed from cells incubated for 20 min in RPMI was differentially screened with yeast (YEPD)‐ and hyphal (RPMI)‐specific probes resuming in identification of a gene expressed in response to culture conditions but not regulated by the yeast‐hyphal transition. The deduced gene product displays significant identity toSaccharomyces cerevisiaeα‐agglutinin, encoded byAGα1, an adhesion glycoprotein that mediates mating of haploid cells. The presence of this gene inC albicansis curious since the organism has not been observed to undergo meiosis. We designate theC. albicansgeneALS1(foragglutinin‐likesequence). While theN‐and C‐termini of the predicted 1260‐amino‐acid ALS1 protein resemble those of the 650‐amino‐acid AGα1, ALS1 contains a central domain of tandem repeats consisting of a highly conserved 36‐amino‐acid sequence not present in AGb1. These repeats are also present on the nucleotide level as a highly conserved 108bp motif. Southern and Northern blot analyses indicate a family ofC. albicansgenes that contain the tandem repeat motif; at least one gene in addition to ALS1 is expressed under conditions similar to those for ALS1 expression. Genomic Southern blots from severalC. albicansisolates indicate that the number of copies of the tandem repeat element in ALS1 differs across strains and. In some cases, between ALS1 alleles in the same strain, suggesting a strain‐dependent variability in ALS1 protein size. Potential roles f

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.tb02219.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryThe valine‐activation domain‐encoding portion of thesrfAlocus(srfA‐d4)is not only involved in the non‐ribosomal synthesis of surfactin, but is also required for the regulation of competence development. In this study we show that impairment of the adenylation activity of the valine‐activating domain did not affect competence development. Deletion analysis and complementation studies delineated the competence‐required portion ofsrfA‐d4to a 168bp fragment, which contains a small open reading frame (ORF), designatedcomS, encoding a polypeptide of 46 amino acids, embedded within, but translated in, a frame different from that ofsrfA‐d4.Introduction of an amber mutation in thecomS‐coding frame prevented competence development, demonstrating the involvement ofcomSin this prokaryotic speci

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.tb02220.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryTheasoAgene of Aeromonas salmonicida is located approximately 7 kb downstream of the A‐layer structural gene, vapA. A 6 kbBamHI fragment containingasoA was cloned and marker‐exchange mutagenesis using a kanamycin‐resistance cassette was performed to generate anasoA mutation in the low‐virulence strain A449L. When analysed by electron microscopy, the mutant A449L‐MB exhibited an altered surface morphology. Strands and blebs of membranous material were observed protruding from the disorganized cell surface. This material was shown to contain lipopolysaccharide and A‐layer subunit protein. The disorganization of the surface of A449L‐IV1B had no apparent effect on virulence when the bacteria were administered to rainbow trout (Oncorhynchus mykiss) by bath Immersion. However, when administered by intraperitoneal injection, the mutant A449L‐MB was found to exhibit significantly increased virulence. The predicted amino acid sequence of AsoA shows homology to a number of polytopic membrane proteins involved in translocation across the cytop

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.tb02221.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryHemophilusinfluenzae type b is a Gram‐negative bacillus that initiates infection by colonizing the upper respiratory tract. Previous studies have established that H. influenzae haemagglutinating pili possess adhesive properties and influence the process of colonization. Additional studies suggest the presence of a secondH. influenzaeadhesin distinct from haemagglulinating pili. In the present study, we examined a non‐piliated H.influenzaetype b strain by transmission electron microscopy and visualized occasional short, thin, surface fibrils. Subsequently, we isolated a spontaneous mutant that lacked surface fibrils and was deficient in adherence to cultured human epithelial cells. Using a cloning strategy that exploited this mutant, we isolated a fragment of DNA that promotesin vitroadherence to human epithelial cells when expressed in laboratory strains of Escherichia coli. Mutagenesis of this fragment in a series ofH. influenzaetype b strains resulted in loss of expression of surface fibrils and a marked decrease in attachment. Furthermore, restoration of surface fibril expression was associated with reacquisition of wild‐type levels of adherence. Our results are consistent with the conclusion thatH. influenzaetype b surface fibrils have adhesive capacity. We speculate that these organelles facilitate colonization of the human respiratory

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.tb02222.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryWe have identified and sequenced anhdcgene in theVibrio anguillarumplasmid pJMl which encodes a histidine decarboxlase enzyme and is an essential component for the biosynthesis of anguibactin. The open reading frame corresponds to a protein of 386 amino acids with a calculated molecular mass of 44 259.69 Da. The amino acid sequence has extensive homology with the pyridoxal‐P‐dependent histidine decarboxylases ofMorganella morganii, Klebsiella planticola, andEnterobacter aerogenes.Tn3‐HoHo1 transposition mutagenesis of thehdcgene present in a recombinant clone carrying the entire pJMI Iron uptake region produced two derivatives, one with thelacZgene in the same orientation as the direction ofhdctranscription and the other with thelacZgene in the opposite orientation. A V.anguillarumstrain harbouring one of the mutated derivatives was unable to grow under iron‐limiting conditions and did not produce anguibactin. Therefore, thehdcgene must play a role in the biosynthetic pathway of this siderophore and consequently in conferring the high virulence phenotype to this bacterium. The role of histidine decarboxylase in biosynthesis of anguibactin was confirmed by the fact that growth under iron starvation was restored by addition of histamine to the medium. The presence of anguibactin was also demonstrated in supernatants from cultures of thehdcmutant strains grown under iron starvation with the addition of histamine, further confirming that histamine is a precursor in the biosynthesis of the siderophore. immunoblot analysis of production of β‐galactosidase byV. anguillarumstrains carrying the lacZ fusions demonstrated that expression of histidine decarboxylase is not regulated by the iron concentration of

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.tb02223.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryA 2.7 kb fragment ofHelicobacter pyloriUA802 chromosomal DNA was cloned and sequenced. Three open reading frames (designated ORF1, oRF2 and ORF3, respectively) were predicted from the DNA sequence, of which ORF1 and ORF2 appeared to be located within the same operon. The deduced 611‐amino‐acid sequence of ORF1, a P‐type ATPase (designated hpCopA), had striking homology (29‐38%) with several bacterial P‐type ATPases and contained the potential functional domains conserved in P‐type ATPases from various sources ranging from bacterial to human. A protein of 66 amino acids (designated hpCopP) encoded by ORF2 shared extensive sequence similarity with MerP, a periplasmic mercuric ion‐transporting protein, and contains the heavy metal‐binding motif. Disruption of ORF1 with a chloramphenicol‐resistance cassette (CAT) rendered theH. pylorimutants more susceptible to cupric ion than their parental strains, whereas there is no significant alternation of susceptibility to Ni2+, Cd2+and Hg2+between the mutants and the parental strains. The results obtained indicate that ORF1 and ORF2 comprise a cation‐transporting system which is associated with copper export out o

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.tb02224.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryThe central (serotype‐specific) Region II of theHaemophilus influenzaeType b capsulation locuscapis 8.3 kb long and contains a cluster of four genes. We show that these genes, designatedorf1toorf4, are involved in the biosynthetic steps required for the formation of the Type b capsular polysaccharide and thatorf1probably encodes a CDP‐ribitolpyrophosphorylase. We present evidence that growth of polysaccharide chains takes place through the alternating addition of single sugar nucleoti

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1995.tb02225.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY