Biomedical subjects

I A Bass

Publications and source records attributed to I A Bass.

At least 19 recordsLinked to original sources

PubMed2006

[Origin, evolution, and migration of drug resistance genes].

Current views on the mechanisms responsible for the emergence of multiple drug resistance in clinical bacterial isolates are considered. Hypotheses on the origin of resistance genes derived from determinants of actinomycetes, antibiotic producers, and chromosomal genes of bacteria involved in cellular metabolism are reviewed. The mechanisms underlying the diffusion of resistance determinants by means of bacterial mobile elements (plasmids, transposons, and integrons) are discussed. Examples of the horizontal transfer of resistance determinants between Gram-positive and Gram-negative bacteria are presented.

Amino Acid Sequence↗

PubMed2005

Activity of Serratia plymuthica IC1270 gene chiA promoter region in Escherichia coli mutants deficient in global regulators of transcription.

To study the regulation of expression of the Serratia plymuthica gene chiA encoding a 58-kDa endochitinase, its 586-bp-long upstream regulatory region was cloned, sequenced and fused to a promoterless lac operon in phage lambdaRS45 to obtain a single-copy transcriptional fusion (P F1chiA )-lac in lysogens of Escherichia coli wild-type strains or their mutants deficient in various global regulators of transcription. The level of P F1chiA -lac expression increased about 20- and 90-fold, respectively, in E. coli K12 Deltahns and double Deltahns stpA mutants deficient in H-NS, and in both H-NS and StpA DNA-binding histone-like proteins, as compared to levels in the wild-type strain. In a Deltalrp mutant deficient in the leucine-responsive transcriptional regulator Lrp, the level of P F1chiA -lac expression increased only up to threefold, whereas even smaller differences relative to the wild-type strain were observed in rpoS and Deltacrp mutants deficient in the sigmaS subunit of RNA polymerase and catabolite-repression protein (CRP), respectively. Deletion of the inverted-repeat sequences and curved DNA regions located in the upstream region of chiA essentially did not influence strain IC1270's chiA promoter activity in E. coli .

Base Sequence↗

PubMed2005

[Activation of the expression of the microcin C51 operon upon glucose starvation of cells at the exponential growth phase].

It was earlier shown that expression of the microcin C51 operon in Escherichia coli cells is activated upon decelerated growth of cells during their transition to the stationary growth phase and depends on the sigmaS subunit of RNA polymerase. Using a single-copy construct containing the cloned promoter region of the microcin C51 operon and a promoterless lac operon (P(mcc)-lac), it was shown that the promoter of the microcin operon was also induced by stress caused by the transition of cells at the exponential growth phase into the medium without glucose as a sole carbon source. Activation of P(mcc)-lac expression upon severe glucose starvation occurred in rpoS+ and rpoS- strains. In cells carrying the rpoD800 mutation that renders the sigma70 subunit of RNA polymerase temperature-sensitive, an activation of P(mcc)-lac expression was observed at nonpermissive temperature, in contrast to its complete inhibition in E. coli cells at the phase of delayed growth. Other stressors-nitrogen starvation, high temperatures, osmotic shock, tetracycline and chloramphenicol-did not activate P(mcc)-lac expression in cells at the exponential growth phase.

Bacteriocins↗

PubMed2004

[Involvement of sigma S and sigma 70 subunits of RNA polymerase and the CRP protein in the regulation of microcin C51 operon expression].

Expression of the microcin C51 operon in Escherichia coli cells is activated during cell entry into the stationary growth phase and depends on the sigmaS subunit of RNA polymerase (RpoS). The null rpoS mutations retained the residual expression level of the transcriptional P(mcc)-lac fusion, which indicates that other sigma subunit can participate in the regulation of transcription of the microcin C51 operon. Data presented in this work show that the overproduction of sigma70 in rpoS- cells diminished the level of P(mcc)-lac expression, as in wild-type cells, which seems to be the consequence of competition between sigma factors for a limited number of core RNA polymerase molecules. In the presence of the rpoD800 mutation that renders sigma70 temperature-sensitive, expression of P(mcc)-lac was not induced in the phase of delayed culture growth at nonpermissive temperature, which indicates that sigma70 is indispensable for microcin operon expression. Point substitutions in the -10 P(mcc) region, leading to the formation of 5'-TGaTATAAT-3' site, enhanced promoter activity but did not affect the relationship between P(mcc)-lac transcription and growth phase, sigmaS, and the activator protein CRP. The activator protein CRP was shown to bind a DNA fragment containing the TGTGA(AATGAA)TCTAT site in the -59.5 bp position relative to the start site of transcription. Mutation in the ssrI gene encoding 6S RNA did not disturb P9mcc)-lac expression; these results indicate that 6S RNA does not participate in the regulation of microcin C51 operon expression.

Bacteriocins↗

PubMed2004

[Distribution of transposons Tn5044 and Tn5070 with unusual mer operons in environmental bacterial populations].

The distribution of unusual mercury resistance transposons, Tn5044 and Tn5070, was examined. A characteristic feature of Tn5044 is temperature sensitivity of its mercury operon and the presence in the mer operon of the gene homologous to RNA polymerase a subunit. Structural organization of mercury operon Tn5070, containing minimum gene set (merRTPA), differs from mer operons of both Gram-negative and Gram-positive bacteria. None of more than two thousand environmental bacterial strains displaying mercury resistance and isolated from the samples selected from different geographical regions hybridized to Tn5040- and Tn5070-specific probes. A concept on the existence of cosmopolite, endemic, and rare transposons in environmental bacterial populations was formulated.

DNA Transposable Elements↗

PubMed2001

[Tn5037-a Tn21-like mercury transposon, detected in Thiobacillus ferrooxidans].

The 6645-bp mercury resistance transposon of the chemolithotrophic bacterium Thiobacillus ferrooxidans was cloned and sequenced. This transposon, named Tn5037, belongs to the Tn21 branch of the Tn21 subgroup, many members of which have been isolated from clinical sources. Having the minimum set of the genes (merRTPA), the mercury resistance operon of Tn5037 is organized similarly to most of the Gram-negative bacteria mer operons and is closest to that of Thiobacillus 3.2. The operator-promoter region of the mer operon of Tn5037 also has the common (Tn21/Tn501-like) structure. However, its inverted, presumably MerR protein binding repeats in the operator/promoter element are two base pairs shorter than in Tn21/Tn501. In the merA region, this transposon shares 77.4, 79.1, 83.2 and 87.8% identical bases with Tn21, Tn501, T. ferrooxidance E-15, and Thiobacillus 3.2, respectively. No inducibility of the Tn5037 mer operon was detected in the in vivo experiments. The transposition system (terminal repeats plus gene tnpA) of Tn5037 was inactive in Escherichia coli K12, in contrast to its resolution system (res site plus gene tnpR). However, transposition of Tn5037 in this host was provided by the tnpA gene of Tn5036, a member of the Tn21 subgroup. Sequence analysis of the Tn5037 res site suggested its recombinant nature.

Base Sequence↗

PubMed2000

[Molecular genetic analysis of the Tn5041 transposition system].

A study was made of the transposition of the mercury resistance transposon Tn5041 which, together with the closely related toluene degradation transposon Tn4651, forms a separate group in the Tn3 family. Transposition of Tn5041 was host-dependent: the element transposed in its original host Pseudomonas sp. KHP41 but not in P. aeruginosa PAO-R and Escherichia coli K12. Transposition of Tn5041 in these strains proved to be complemented by the transposase gene (tnpA) of Tn4651. The gene region determining the host dependence of Tn5041 transposition was localized with the use of a series of hybrid (Tn5041 x Tn4651) tnpA genes. Its location in the 5'-terminal one-third of the transposase gene is consistent with the data that this region is involved in the formation of the transposition complex in transposons of the Tn3 family. As in other transposons of this family, transposition of Tn5041 occurred via cointegrate formation, suggesting its replicative mechanism. However, neither of the putative resolution proteins encoded by Tn5041 resolved the cointegrates formed during transposition or an artificial cointegrate in E. coli K12. Similar data were obtained with the mercury resistance transposons isolated from environmental Pseudomonas strains and closely related to Tn5041 (Tn5041 subgroup).

Base Sequence↗

PubMed1998

Horizontal spread of mer operons among gram-positive bacteria in natural environments.

Horizontal dissemination of the genes responsible for resistance to toxic pollutants may play a key role in the adaptation of bacterial populations to environmental contaminants. However, the frequency and extent of gene dissemination in natural environments is not known. A natural horizontal spread of two distinct mercury resistance (mer) operon variants, which occurred amongst diverse Bacillus and related species over wide geographical areas, is reported. One mer variant encodes a mercuric reductase with a single N-terminal domain, whilst the other encodes a reductase with a duplicated N-terminal domain. The strains containing the former mer operon types are sensitive to organomercurials, and are most common in the terrestrial mercury-resistant Bacillus populations studied in this work. The strains containing the latter operon types are resistant to organomercurials, and dominate in a Minamata Bay mercury-resistant Bacillus population, previously described in the literature. At least three distinct transposons (related to a class II vancomycin-resistance transposon, Tn1546, from a clinical Enterococcus strain) and conjugative plasmids are implicated as mediators of the spread of these mer operons.

Bacillus↗

PubMed1997

Tn5041: a chimeric mercury resistance transposon closely related to the toluene degradative transposon Tn4651.

This paper reports the discovery and characterization of Tn5041, a novel-type transposon vehicle for dissemination of mercury resistance in natural bacterial populations. Tn5041 (14876 bp), identified in a Pseudomonas strain from a mercury mine, is a Tn3 family mercury resistance transposon far outside the Tn21 subgroup. As in other Tn3 family transposons, Tn5041 duplicates 5 bp of the target sequence following insertion. Tn5041 apparently acquired its mer operon as a single-ended relic of a transposon belonging to the classical mercury resistance transposons of the Tn21 subgroup. The putative transposase and the 47 bp terminal inverted repeats of Tn5041 are closely related to those of the toluene degradative transposon Tn4651 and fall into a distinct subgroup on the fringe of the Tn3 family. The amino acid sequence of the putative resolvase of Tn5041 resembles site-specific recombinases of the integrase family. Besides the mer operon and putative transposition genes, Tn5041 contains a 4 kb region that accommodates a number of apparently defective genes and mobile elements.

Amino Acid Sequence↗

PubMed1995

Four genes, two ends, and a res region are involved in transposition of Tn5053: a paradigm for a novel family of transposons carrying either a mer operon or an integron.

The complete nucleotide sequence of an 8447 bp-long mercury-resistance transposon (Tn5053) has been determined. Tn5053 is composed of two modules: (i) the mercury-resistance module and (ii) the transposition module. The mercury-resistance module carries a mer operon, merRTPFAD, and appears to be a single-ended relic of a transposon closely related to the classical mercury-resistance transposons Tn21 and Tn501. The transposition module of Tn5053 is bounded by 25 bp terminal inverted repeats and contains four genes involved in transposition, i.e. tniA, tniB, tniQ, and tniR. Transposition of Tn5053 occurs via cointegrate formation mediated by the products of the tniABQ genes, followed by site-specific cointegrate resolution. This is catalysed by the product of the tniR gene at the res region, which is located upstream of tniR. The same pathway of transposition is used by Tn402 (Tn5090) which carries the integron of R751. Transposition genes of Tn5053 and Tn402 are interchangeable. Sequence analysis suggests that Tn5053 and Tn402 are representatives of a new family of transposable elements, which fall into a recently recognized super-family of transposons including retroviruses, insertion sequences of the IS3 family, and transposons Tn552 and Tn7. We suggest that the tni genes were involved in the dissemination of integrons.

Amino Acid Sequence↗

PubMed1990

[A family of repeated sequences in Drosophila genome with telomeric localization: properties and polymorphism].

The previously cloned Drosophila genome fragment Dm665 (2.4 kb) hybridizing with telomers on polytene chromosomes is a representative of the family of repeats, a part of which being organized in tandem clusters. The repeats are not transcribed in cell culture, are species-specific and represented in 200-250 copies per haploid genome. In natural and laboratory Drosophila lines polymorphism has been revealed with regard to homology with Dm665 in the telomeres.

Animals↗

PubMed1990

[Spontaneous transformation in mixed cultures of various types of Acinetobacter and during joint growth of Acinetobacter calcoaceticus with Escherichia coli and Pseudomonas aeruginosa].

The transfer of chromosomal and plasmid genes was studied via spontaneous transformation is mixed cultures of Acinetobacter spp. It turned out that any Acinetobacter strain, irrespective of its species specificity, serves as chromosomal DNA donor in case the mixed culture contains competent cells of the recipient strain. No transfer took place when non-related bacteria were used as donors. We also studied the transfer into Ac. calcoaceticus competent strain cells of small non-conjugative plasmids having broad host range (RSF1010, pAK1). In these cases, DNA donors could be not only acinetobacters of other species, but bacteria belonging to other systematic groups (families)--E. coli and P. aeruginosa. The transfer of plasmids from cells of unrelated bacteria took place with a frequency of about 10(-5)-10(-6). The possible role of spontaneous transformation in horizontal gene transfer is discussed.

Acinetobacter↗

PubMed1990

[Hoppel-family of mobile elements of Drosophila melanogaster, flanked by short inverted repeats and having preferential localization in the heterochromatin regions of the genome].

A mobile element (ME) having 91% homology with Dm1360 (Kholodilov et al., 1987) has been cloned from the Drosophila melanogaster genome and sequenced. The family of ME was designated hoppel. The members of this family are flanked by short inverted repeats likewise P, hobo and HB. The hoppel is hybridized with 10-30 euchromatic sites of polytene chromosomes of different Drosophila stocks. Abundant hybridization with heterochromatic regions of chromosomes-chromocenter, pericentric heterochromatin, the 4 chromosome and telomeres was observed in all stocks of D. melanogaster examined and in D. simulans. At least six genomic variants of ME differing in length of the central part were revealed. Hoppel possesses ARS activity similar to the P element. Two ME hoppel were shown to be arranged as a direct repeat in the recombinant phage.

Animals↗

PubMed1989

[Deletion-insertion mapping of the region non-essential for functioning of the beta-subunit of Escherichia coli RNA polymerase].

A plasmid has been constructed containing the gene of beta-subunit of RNA polymerase of Escherichia coli under control of the PR promoter of bacteriophage lambda. PR promoter may be induced by heating up to 42 degrees C. In frame insertions of different sequences between 989 and 990 or 1010 and 1011 codons of the rpoB gene do not inactivate the beta-subunit function. Deletions in the region of 1011-1027 codons result in inactivation of beta-subunit. We localized antigene determinant of monoclonal anti-beta-antibodies which do not inactivate RNA polymerase in vitro. The borders of non-essential region of beta-subunit were accurately determined.

Bacteriophage lambda↗

PubMed1987

[Transfer of "artificial transposons" constructed on the basis of insertion element IS1].

Terminal inverted repeats of the insertion element IS1 were synthesized chemically and plasmids containing these sequences flanking kanamycin-resistance gene in different combinations were constructed. Further incorporation of a whole-sized copy of the IS1 into such plasmids caused in some cases the autonomous transfer of Km-resistance from plasmid to bacteriophage lambda DNA. The transposition of the Km-resistance gene was only observed in those cases when the gene was enclosed between IS1 copy and one of the terminal repeats. The data obtained are discussed with regard to the evolution of bacterial transposons.

Bacteriophage lambda↗

PubMed1984

[Dominant mutations of rifampicin resistance in Escherichia coli K-12].

Significant portion (up to 20%) of dominant mutations (rifd mutations) was observed among spontaneous mutations of rifampicin resistance picked up in cells of haploid Escherichia coli strain. These mutations are similar to rifd mutations obtained earlier when selecting them in rif-s/rif-s merodiploids. On the basis of analysis of nucleotide substitutions taking place in formation of spontaneous and induced mutations, it is established that rifd mutations are caused by single nucleotide substitution. The majority of rifd mutations are localized in a small region of the central part of RNA polymerase beta-subunit gene covering less than 200 base pairs. A rifd mutant has been described which occurred as a result of micro-deletion in one of the "hot" spots of the central region of beta-subunit gene.

Amino Acid Sequence↗

PubMed1983

RNA polymerase rifampicin resistance mutations in Escherichia coli: sequence changes and dominance.

Five recombinant plasmids, pBK2646, pBK611, pRC3, pRC4 and pRC5, carrying rpoB rifampicin-resistant RNA-polymerase genes were obtained. The sequence analysis of these plasmids revealed certain structural changes in the rpoB gene which specify corresponding alterations in the beta-subunit of RNA polymerase. Some functional properties of the corresponding mutant strains and their RNA polymerases have been investigated.

Base Sequence↗

PubMed1981

Primary structure of Escherichia coli RNA polymerase nucleotide substitution in the beta subunit gene of the rifampicin resistant rpoB255 mutant.

The transducing phage lambda dsupM814 and the plasmid pIB1830 containing the wild-type rpoB gene have been constructed and the primary structure of the gene's central fragment has been established. In contrast with the wild-type, the gene of the rpoB255 mutant, whose primary structure has been published, was found to contain an A.T. leads to T.A. transversion entailing the substitution of a valine residue for the aspartic acid residue (516) of the wild-type beta subunit.

Base Sequence↗