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Volume 147,
Issue 6,
2001
Volume 147, Issue 6, 2001
- Review Article
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- Microbiology Comment
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- Antigens And Immunity
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The role of antibodies to Bacillus anthracis and anthrax toxin components in inhibiting the early stages of infection by anthrax spores
More LessVaccines which are efficacious against anthrax, such as the human vaccine, Anthrax Vaccine Absorbed (AVA), contain the protective antigen (PA) component of the anthrax toxins as the major protective immunogen. Although AVA protects against inhalational anthrax, the immune responses to and role in protection of PA and possibly other antigens have yet to be fully elucidated. Sera from animals immunized with a toxin-producing, unencapsulated live vaccine strain of Bacillus anthracis have been reported to have anti-spore activities associated with the antitoxin humoral response. The authors performed studies to determine whether anti-PA antibody (Ab)-containing preparations stimulated spore uptake by phagocytes and suppressed the germination of spores in vitro. AVA- and PA-immune sera from several species enhanced the phagocytosis by murine peritoneal macrophages of spores of the virulent Ames and the Sterne vaccine strains. Antitoxin Abs appeared to contribute significantly, although not solely, to the enhanced uptake. Rabbit antisera to PA purified from either Sterne or a PA-producing pX01-cured recombinant, affinity-purified anti-PA IgG, and monkey antisera to AVA were used to assess the role of anti-PA Abs. Rabbit anti-PA Abs promoted the uptake of spores of the PA-producing strains Sterne, Ames and RP42, a mutant of Sterne producing only PA, but not of the pX01-ΔSterne-1 strain, ΔAmes strain, or RP4, a mutant of Sterne with deletions in the loci encoding PA and the oedema factor (EF) toxin component and producing only the lethal factor toxin component. Rabbit anti-PA and monkey anti-AVA Abs also significantly inhibited spore germination in vitro compared to preimmune serum or medium. Spore-associated proteins recognized by anti-PA Abs were detected by electron microscopy and confirmed by immunoblotting of spore coat extracts. Thus, the anti-PA Ab-specific immunity induced by AVA has anti-spore activity and might have a role in impeding the early stages of infection with B. anthracis spores.
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- Biochemistry
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A peptidorhamnomannan from the mycelium of Pseudallescheria boydii is a potential diagnostic antigen of this emerging human pathogen
More LessThe ascomycete Pseudallescheria boydii is an emerging human pathogen frequently found in soil and polluted water. A peptidopolysaccharide antigen has been isolated from mycelial forms of P. boydii, and characterized using chemical and immunological methods. Monosaccharide composition, methylation analysis, and 1H- and 13C-NMR spectra indicated the presence of a rhamnomannan with a structure distinct from those of similar components isolated from other fungi, containing Rhap(1→3)Rhap epitopes on side chains which may be linked (1→3) to (1→6)-linked mannose. The peptidorhamnomannan from P. boydii reacted poorly with an antiserum raised against whole cells of Sporothrix schenckii and strongly with one against P. boydii hyphae. These characteristics and immunological differences suggest that this major rhamnose-containing antigen of P. boydii may be useful for the specific diagnosis of infections attributable to this fungus.
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A pre-genetic study of the isoforms of malic enzyme associated with lipid accumulation in Mucor circinelloides
More LessThe oleaginous fungus Mucor circinelloides possesses at least six isoforms of malic enzyme (EC 1.1.1.40), a key lipogenic enzyme in filamentous fungi. These isoforms were detected using a specific stain for activity after native PAGE of cell extracts. Only one isoform (isoform IV) was associated with lipid accumulation, appearing only after N-exhaustion from the medium (which is a pre-requisite for lipid accumulation) in glucose-growing cells. Isoforms I, II, V and VI were involved in anaerobic growth and only appeared under O2-limited conditions. Isoform III appeared to be constitutive and was formed under conditions of active (balanced) growth and is therefore thought to play a crucial role in basic metabolism. Growth on acetate increased the amount of cell lipid (from 25–27% in glucose-grown cells to 37–38% in acetate-grown cells) accumulated by M. circinelloides and this was associated with the appearance of isoform IV of malic enzyme prior to N-exhaustion in these cultures. Amino acid sequence analysis of isoforms III and IV suggests that these two malic enzymes may be encoded by a single gene and that isoform IV is formed from isoform III by post-translational modification initiated by either N-limitation (when glucose was the carbon source) or growth on acetate as the sole carbon source.
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Involvement of a transformylase enzyme in siderophore synthesis in Pseudomonas aeruginosa
More LessThe GenBank accession number for the sequence reported in this paper is U07359.
Fluorescent pseudomonads produce yellow-green siderophores when grown under conditions of iron starvation. Here, the characterization of the pvdF gene, which is required for synthesis of the siderophore pyoverdine by Pseudomonas aeruginosa strain PAO1, is described. A P. aeruginosa pvdF mutant was constructed and found to be defective for production of pyoverdine, demonstrating the involvement of PvdF in pyoverdine synthesis. Transcription analysis showed that expression of pvdF was regulated by the amount of iron in the growth medium, consistent with its role in siderophore production. DNA sequencing showed that pvdF gives rise to a protein of 31 kDa that has similarity with glycinamide ribonucleotide transformylase (GART) enzymes involved in purine synthesis from a wide range of eukaryotic and prokaryotic species. Chemical analyses of extracts from wild-type and pvdF mutant bacteria indicated that the PvdF enzyme catalyses the formylation of N 5-hydroxyornithine to give rise to N 5-formyl-N 5-hydroxyornithine, a component of pyoverdine. These studies enhance understanding of the enzymology of pyoverdine synthesis, and to the best of the authors’ knowledge provide the first example of involvement of a GART-type enzyme in synthesis of a secondary metabolite.
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Substrate analysis and molecular cloning of the extracellular alkaline phosphatase of Streptomyces griseus
More LessThe GenBank accession number for the sequence reported in this paper is AJ278740.
Streptomyces species secrete large amounts of alkaline phosphatase (AP) enzymes that have not been characterized so far. An AP has been purified to homogeneity from cultures of Streptomyces griseus IMRU 3570. The enzyme has a monomer size of 62 kDa and is processed in the culture to a 33 kDa protein as shown by immunoblotting. The enzyme was purified by ammonium sulfate precipitation, CM-Sephadex cationic exchange, chromatofocusing and HPLC Sphaerogel 3000SW filtration. The pure enzyme uses a variety of organic phosphorylated compounds as substrates. The N-terminal end of the mature protein was found to be RLREDPFTLGVASGDPHP. The gene phoA has been cloned using as probe an oligomer based on the N-terminal sequence of the S. griseus AP. phoA encodes a protein of 62678 Da with low homology to the AP of Escherichia coli. The phoA gene was found to be homologous to three alkaline-phosphatase-encoding genes previously identified in the Streptomyces coelicolor genome. On the basis of the optimal pH, substrate specificity and differences in amino acid sequence of motifs defining the active centre of APs, the S. griseus AP uses a wide range of organic phosphate substrates and is different from the phosphatases of Gram-negative bacteria.
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- Biotechnology
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A novel glycosylated Cu/Zn-containing superoxide dismutase: production and potential therapeutic effect
The fungal strain Humicola lutea 103 produces a naturally glycosylated Cu/Zn SOD. To improve its yield, the effect of an increased concentration of dissolved oxygen (DO) on growth and enzyme biosynthesis by the producer, cultivated in a 3 l bioreactor, was examined. Exposure to a 20% DO level caused a 1·7-fold increase of SOD activity compared to the DO-uncontrolled culture. Maximum enzyme productivity of SOD was approximately 300×103 U (kg wet biomass)−1. The novel enzyme was purified to electrophoretic homogeneity. The presence of Cu and Zn were confirmed by atomic absorption spectrometry. The molecular mass of H. lutea Cu/Zn SOD was calculated to be 31870 Da for the whole molecule and 15936 Da for the structural subunits. The N-terminal sequence revealed a high degree of structural homology with Cu/Zn SOD from other prokaryotic and eukaryotic sources. H. lutea Cu/Zn SOD was used in an in vivo model for the demonstration of its protective effect against myeloid Graffi tumour in hamsters. Comparative studies revealed that the enzyme (i) elongated the latent time for tumour appearance, (ii) inhibited tumour growth in the early stage of tumour progression (73–75% at day 10) and (iii) increased the mean survival time of Graffi-tumour-bearing hamsters. Moreover, the fungal Cu/Zn SOD exhibited a strong protective effect on experimental influenza virus infection in mice. The survival rate increased markedly, the time of survival rose by 5·2 d and the protective index reached 86%. The H. lutea SOD protected mice from mortality more efficiently compared to the selective antiviral drug ribavirin and to commercial bovine SOD. In conclusion, our results suggest that appropriate use of the novel fungal SOD, applied as such or in combination with selective inhibitors, could outline a promising strategy for the treatment of myeloid Graffi tumour and influenza virus infection.
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A two-hybrid system based on chimeric operator recognition for studying protein homo/heterodimerization in Escherichia coli
More LessThe development of a convenient and promising alternative to the various two-hybrid methods that are used to study protein–protein interactions is described. In this system, a lambdoid chimeric operator is recognized by a hybrid repressor formed by two chimeric monomers whose C-terminal domains are composed of heterologous proteins (or protein domains). Only if these proteins efficiently dimerize in vivo is a functional repressor formed able to bind the chimeric operator and shut off the synthesis of a downstream reporter gene. This new approach was tested with several interacting proteins ranging in size from less than 100 to more than 800 amino acids and, to date, no size or topology limit has been detected.
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- Development And Structure
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Visualization of Borrelia burgdorferi sensu lato by fluorescence in situ hybridization (FISH) on whole-body sections of Ixodes ricinus ticks and gerbil skin biopsies
More LessThe objective of this study was to visualize borreliae directly in whole-body sections of Ixodes ricinus by fluorescence in situ hybridization (FISH). Borrelia afzelii mono-infected or Borrelia burgdorferi sensu stricto (ss)/B. afzelii double-infected nymphs were fixed, embedded in cold polymerizing resin and sectioned. The same sample processing was applied to skin biopsies taken from a Mongolian gerbil after an infectious tick-bite. FISH was carried out using 16S-rRNA-directed, fluorescence-labelled oligonucleotide probes specific for the genus Borrelia and specific within the group of Lyme borreliosis-associated genospecies B. afzelii, B. burgdorferi ss, Borrelia garinii and Borrelia valaisiana. Sensitivity and specificity of the newly designed probes were evaluated using PCR, dot-blot hybridizations and FISH. Despite significant autofluorescence of certain tick tissues (which allowed good histological orientation within the sections), borreliae showing the typical spirochaetal morphotype were clearly visible in five out of six putatively infected ticks. These findings were confirmed by electron microscopy of ticks from the same infected batch as used for FISH. Attempts to produce ticks infected by two different Borrelia genospecies were not successful. FISH on whole-body sections of resin-embedded ticks offers the possibility of visualizing and identifying borreliae within tick tissues. This technique has great potential for the investigation of the transmission of bacteria or other micro-organisms by arthropod vectors. Furthermore, clear visualization of single spirochaetes distributed along subcutaneous fat cell membranes in gerbil skin biopsies suggests that FISH might also be suitable for the detection of borreliae in clinical tissue specimens.
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Cell cycle control of septin ring dynamics in the budding yeast
More LessSeptins constitute a cytoskeletal structure that is conserved in eukaryotes. In Saccharomyces cerevisiae, the Cdc3, Cdc10, Cdc11, Cdc12 and Shs1/Sep7 septins assemble as a ring that marks the cytokinetic plane throughout the budding cycle. This structure participates in different aspects of morphogenesis, such as selection of cell polarity, localization of chitin synthesis, the switch from hyperpolar to isotropic bud growth after bud emergence and the spatial regulation of septation. The septin cytoskeleton assembles at the pre-bud site before bud emergence, remains there during bud growth and duplicates at late mitosis eventually disappearing after cell separation. Using a septin-GFP fusion and time-lapse confocal microscopy, we have determined that septin dynamics are maintained in budding zygotes and during unipolar synchronous growth in pseudohyphae. By means of specific cell cycle arrests and deregulation of cell cycle controls we show that septin assembly is dependent on G1 cyclin/Cdc28-mediated cell cycle signals and that the small GTPase Cdc42, but not Rho1, are essential for this event. However, during bud growth, the septin ring shapes a bud-neck-spanning structure that is unaffected by failures in the regulation of mitosis, such as activation of the DNA repair or spindle assembly checkpoints or inactivation of the anaphase-promoting complex (APC). At the end of the cell cycle, the splitting of the ring into two independent structures depends on the function of the mitotic exit network in which the protein phosphatase Cdc14 participates. Our data support a role of cell cycle control mechanisms in the regulation of septin dynamics to accurately coordinate morphogenesis throughout the budding process in yeast.
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Identification of lipopolysaccharide O antigen synthesis genes required for attachment of the S-layer of Caulobacter crescentus
The GenBank accession number for the NA1000 rsaADEF and gmd, per, wbqA, wbqR, wbqX and wbqZ sequences reported in this paper is AF06235.
Peter Awram and John SmitThe outer surface of Caulobacter crescentus consists of a two-dimensional crystalline protein lattice layer (S-layer). A fraction of the LPS has an O antigen polymer attached to the core to form a ‘smooth’ LPS (S-LPS), which is required for attachment of the protein S-layer to the outer-membrane surface. A method to screen for strains defective in LPS production, based on loss ofS-layer attachment, was developed and applied to libraries of transposon-generated mutants. Eighteen distinct insertions were found with transposon interruptions in genes affecting S-LPS production, 12 of which were located near the S-layer subunit protein gene, rsaA, and its transporter genes. Sequence adjacent to transposon insertion points was determined and used to search a C. crescentus genome database. Twelve ORFs likely to be involved in S-LPS synthesis were identified. Seven of the predicted ORFs were linked to rsaA. Six of the putative genes had identity with proteins involved in synthesis of sugar residues, including five predicted to make perosamine. The remaining six ORFs were similar to glycosyltransferases involved in forming linkages between sugar residues in the O antigen, while one may be a transcription repressor. Other chemical and preliminary proton NMR studies of the S-LPS O antigen indicate that it contains an N-acetylated 4,6-dideoxy-4-aminohexose, but is not assembled as a simple, uniform homopolymer, consisting of several different linkages between sugar residues. The ORFs described here include homologues of all the enzymes involved in the synthesis of N-acetylperosamine, a 4,6-dideoxy-4-aminohexose. Overall, the data are consistent with the hypothesis that the O antigen of C. crescentus S-LPS consists primarily of N-acetylperosamine residues polymerized with multiple anomeric linkages.
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- Genetics And Molecular Biology
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Cloning and functional analysis of a phosphopantetheinyl transferase superfamily gene associated with jadomycin biosynthesis in Streptomyces venezuelae ISP5230
More LessThe GenBank accession numbers for the jadM and jadNOX sequences reported in this paper are AF222693 and AY026363, respectively.
Sequence analysis of a XhoI/SacI fragment of chromosomal DNA downstream of jadL in the Streptomyces venezuelae ISP5230 gene cluster for jadomycin biosynthesis detected a partial ORF similar in its deduced amino acid sequence to the hetI product involved in synthesizing a regulator of heterocyst spacing in Anabaena. By probing a phage library of S. venezuelae DNA with the XhoI/SacI fragment, the authors identified and isolated a hybridizing clone. The nucleotide sequence of its DNA contained three complete ORFs (jadM, N and X) and one incomplete ORF (jadO). The jadM ORF lay immediately downstream of, and partially overlapped, jadL. It contained 786 nucleotides encoding an amino acid sequence like those of enzymes in the phosphopantetheinyl transferase family. The jadN ORF contained 1794 nucleotides and encoded an amino acid sequence resembling acyl-CoA decarboxylases, thus suggesting a role in polyketide condensation reactions.The jadX ORF was not identified, but the partial jadO showed marked similarities in its deduced amino acid sequence to NDP-hexose-2,3-dehydratases, indicating a role in forming the sugar component of jadomycin B. Expression of jadM in Escherichia coli and examination of the product by SDS-PAGE established that the ORF encoded a 29·1 kDa protein, corresponding in size to the 262 amino acid polypeptide deduced from the jadM sequence. Evidence from a Northern hybridization indicated that jadM expression is correlated with jadomycin B synthesis. Cultures of S. venezuelae ISP5230 disrupted in jadM produced only 2–5% of the wild-type titre of jadomycin B, but grew well and produced chloramphenicol normally. The authors conclude that jadM encodes a holo-ACP synthase needed primarily for jadomycin B biosynthesis.
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Structure of the ask-asd operon and formation of aspartokinase subunits in the cephamycin producer ‘Amycolatopsis lactamdurans’
More LessThe GenBank accession number for the sequence reported in this paper is AJ298904.
The first two genes of the lysine pathway are closely linked forming a transcriptional operon in the cephamycin producer ‘Amycolatopsis lactamdurans’. The asd gene, encoding the enzyme aspartic semialdehyde dehydrogenase, has been cloned by complementation of Escherichia coli asd mutants. It encodes a protein of 355 aa with a deduced M r of 37109. The ask gene encoding the aspartokinase (Ask) is located upstream of the asd gene as shown by determination of Ask activity conferred to E. coli transformants. asd and ask are separated by 2 nt and are transcribed in a bicistronic 2·6 kb mRNA. As occurs in corynebacteria, the presence of a ribosome-binding site within the ask sequence suggests that this ORF encodes two overlapping proteins, Askα of 421 aa and M r 44108, and Askβ of 172 aa and M r 18145. The formation of both subunits of Ask from a single gene (ask) was confirmed by using antibodies against the C-terminal end of Ask which is identical in both subunits. Ask activity of ‘A. lactamdurans’ is regulated by the concerted action of lysine plus threonine and this inhibition is abolished in E. coli transformants containing Ser301 to Tyr, or Gly345 to Asp mutations of the ‘A. lactamdurans’ ask gene.
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Unique expression of a highly conserved mycobacterial gene in IS901 + Mycobacterium avium
More LessThe GenBank accession number for the p40 gene, together with 542 bp upstream sequence, is AF247653.
Expression of a gene encoding a novel protein antigen of 40 kDa (p40) was detected in IS901 + strains of Mycobacterium avium, but not in any other species or subspecies of Mycobacterium tested, including IS901 − M. avium and the other members of the M. avium complex. Although Southern hybridization revealed that the p40 gene is widely distributed within the genus, expression of the antigen could not be detected on Western blots of mycobacterial cell lysates. Nucleotide sequence analysis of the cloned p40 gene, and a database search, revealed high levels of sequence identity with a homologous gene in IS901 − M. avium, M. avium subsp. paratuberculosis, Mycobacterium bovis, Mycobacterium leprae, Mycobacterium smegmatis and Mycobacterium tuberculosis. Further analysis of upstream sequences identified a putative promoter region. The p40 gene is the first example of a gene that is widely distributed within the genus Mycobacterium but expressed only in association with the presence of a genomic insertion element, in this case IS901, in strains of M. avium isolated from birds and domestic livestock.
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Genetic localization and regulation of the maltose phosphorylase gene, malP, in Lactococcus lactis
More LessThe GenBank accession number for the sequence reported in this paper is AF327721.
Maltose phosphorylase (MP) from Lactococcus lactis was purified and the corresponding gene was cloned and expressed in Escherichia coli. The isoelectric point of the pure enzyme was determined to be 7·0. According to zymogram analysis and SDS-PAGE, the native MP was shown to be a monomeric enzyme with a molecular mass of 75 kDa. A polyclonal antiserum was produced to assess the regulation of the gene encoding MP in Lc. lactis. According to immunoblot analysis, synthesis of the enzyme was markedly repressed by both glucose and lactose in the growth medium. When the lactococci were cultivated in the presence of other sugars, including maltose, trehalose or galactose, there was a pronounced expression of the MP gene. In addition, when the cells were grown in media without any added sugar, there was also pronounced expression of the enzyme, according to immunoblot analysis and specific activity data. These results indicated that no particular sugar specifically induces the gene encoding MP. However, an effect of glucose on MP expression was demonstrated by performing fermentations in the presence of both maltose and glucose. When glucose was added to maltose-grown lactococci in the mid-exponential growth phase, both the specific activity and amount of MP per millilitre of cell extract decreased rapidly. The genetic locus for the MP gene was found to be in the vicinity of the region encoding a possible regulator belonging to the LacI-GalR family of transcriptional regulators. Furthermore, this genetic location was separated from the previously characterized maltose-inducible and glucose-repressible β-phosphoglucomutase (β-PGM) gene. The different genetic loci for the genes encoding MP and β-PGM explains the different gene regulation behaviour.
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Analysis of σ54-dependent genes in Enterococcus faecalis: a mannose PTS permease (EIIMan) is involved in sensitivity to a bacteriocin, mesentericin Y105
More LessThe σ54 RNA polymerase subunit has a prominent role in susceptibility of Listeria monocytogenes and Enterococcus faecalis to mesentericin Y105, a class IIa bacteriocin. Consequently, σ54-dependent genes as well as specific activators also required for expression of these genes were sought. Five putative σ54-associated activators were detected in the genome of E. faecalis V583, and all but one could activate the transcription of permease genes belonging to sugar phosphotransferase systems (PTSs). Interestingly, these activators display a helicase signature not yet reported in this activator family, which could explain the ATP-dependent mechanism of DNA unwinding preceding the start of transcription. To find which activator is linked to susceptibility of E. faecalis to mesentericin Y105, their respective genes were subsequently interrupted. Among them, only mptR gene interruption led to a resistance phenotype. Immediately downstream from mptR, a putative σ54-dependent operon was found to encode a mannose PTS permease, namely . Moreover, in liquid culture, glucose and mannose induced the sensitivity of E. faecalis to mesentericin Y105. Since sugars have previously been reported to induce PTS permease expression, it appears that expression, presumably induced in the presence of glucose and mannose, leads to an enhanced sensitivity of E. faecalis to the bacteriocin. Additional information was gained from knockouts within the permease operon. Interruption of the distal mptD gene, which encodes the IID subunit of , strikingly led to resistance to mesentericin Y105. Moreover, MptD appears to be a peculiar membrane subunit, bearing an additional domain compared to most known IID subunits. According to these results, is clearly involved in susceptibility to mesentericin Y105 and could even be its receptor at the E. faecalis surface. Finally, it is hypothesized that MptD could be responsible for the targeting specificity, via an interaction between its additional domain and mesentericin Y105.
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Suppression of thermosensitive peptidyl-tRNA hydrolase mutation in Escherichia coli by gene duplication
More LessPeptidyl-tRNA hydrolase (Pth) in Escherichia coli is required to recycle tRNA molecules that dissociate from the ribosome as peptidyl-tRNA during protein synthesis. At non-permissive temperatures, strains with a thermosensitive mutation affecting the enzyme accumulate peptidyl-tRNA, cease protein synthesis and die. The rate of reversion of this mutation to thermoresistance varies widely according to the genetic background of the cell and the temperature of selection; under certain conditions, reversion can occur at rates approaching 10−3 per cell per generation. In such revertants, a chromosomal pth gene can be replaced by an inactivated gene, restoring thermosensitive growth in most cases. PCR amplification experiments and Southern blots show the presence of both normal and inactivated copies of the gene, demonstrating that gene duplication has occurred in the revertants. Estimation of intracellular peptidyl-tRNA hydrolase by Western blotting confirms this explanation of the mechanism of high-frequency reversion to thermoresistance.
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Characterization of two autoreplicative regions of the IncHI2 plasmid R478: RepHI2A and RepHI1A(R478)
More LessThe GenBank accession numbers for the sequences reported in this paper are U62006 (RepHI2A) and U62007 (RepHI1A(R478)).
Plasmids of the incompatibility groups HI and HII (IncH plasmids) generally confer multiple antibiotic resistances upon their host pathogenic strain. IncHI group plasmids are distinguished by their property of optimal transfer by conjugation at temperatures below 30 °C, allowing for the spread of multiple antibiotic resistance outside their host natural environment, the gut. Plasmids of the IncHI1 subgroup encode multiple replicons. In the present study it is shown that the prototype IncHI2 subgroup plasmid, R478, contains at least two iteron-controlled autoreplicative regions, RepHI2A and RepHI1A(R478). The DNA sequence and the molecular characteristics of each replicon region are described. RepHI2A is unique to plasmids of the IncHI2 subgroup and contains an unusually large number of iteron sequences downstream of the replication initiator gene. The nucleotide sequence of the replication initiator gene and of the iterons within RepHI1A(R478) show very close similarity with those of the previously reported RepHI1A replicon of the IncHI1 subgroup plasmid R27. The presence of RepHI1A(R478) on R478 most likely accounts for the observed incompatibility between R478 and plasmids of the IncHI1 subgroup. These are the first autoreplicative regions from an IncHI2 subgroup plasmid to be described.
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