[Distribution of transposons Tn5044 and Tn5070 with unusual mer operons in environmental bacterial populations]. / Raspostranenie v prirodnykh populiatsiiakh bacterii transpozonov Tn5044 i Tn5070, nesushchikh nekanonicheskie mer-operony.

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.

[Mercury-resistant bacteria from permafrost sediments and prospects for their use in comparative studies of mercury resistance determinants]. / Rezistentnye k soedineniiam rtuti bakterii iz mnogoletnemerzlykh otlozhenii i perspektivy ikh ispol'zovaniia v sravnitel'nykh issledovaniiakh determinant rtut'-ustoichivosti.

Mercury-resistant bacteria were isolated from permafrost sediments of Kolyma lowland and Canada existing over five thousand to two million years. Their content was shown to vary within the range 0.001-2.9% and to depend on the amount of mercury in sampling sites (coefficient of correlation 0.75). A collection of mercury-resistant bacterial strains was created. In this collection, various representatives of both Gram-positive bacteria (Bacillus, Exiguobacterium, Micrococcus, Arthrobacter) and Gram-negative bacteria (Pseudomonas, Acinetobacter, Plesiomonas, Myxobacteriales) were identified. Most resistant bacteria were found to contain determinants homologous to mer-operons of contemporary bacteria. The isolated strains of paleobacteria are proposed to be used for a comparative structural study of contemporary and ancient plasmids and transposons carrying mercury resistance determinants.

[Horizontal transfer of mercury resistance genes in natural bacterial populations]. / Gorizontal'nyi perenos genov ustoichivosti k soedineniiam rtuti v prirodnykh populiatsiiakh bakterii.

The results of studying the horizontal transfer of mercury resistance determinants in environmental bacterial populations are reviewed. Identical or highly homologous mercury resistance (mer) operons and transposons were found in bacteria of different taxonomic groups from geographically distant regions. Recombinant mer operons and transposons were revealed. The data suggest high frequencies of horizontal transfer and of recombination for mercury resistance determinants. The mechanisms of horizontal gene transfer were elucidated in Gram-negative and Gram-positive bacteria. New transposons were found and analyzed.

[Tn5037-a Tn21-like mercury transposon, detected in Thiobacillus ferrooxidans]. / Tn5037-Tn21-podobnyi rtutnyi transpozon, obnaruzhennyi u 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.

[Molecular genetic analysis of the Tn5041 transposition system]. / Molekuliarno-geneticheskii analiz sistemy transpozitsii Tn5041.

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).

[Deletion-insertion mapping of the region non-essential for functioning of the beta-subunit of Escherichia coli RNA polymerase]. / Deletsionno-insertsionnoe kartirovanie oblasti, ne sushchestvennoi dlia funktsionirovaniia beta-sub"edinitsy RNK-polimerazy Escherichia coli.

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.

[Study of the horizontal transfer of mercury resistance genes in natural populations of bacteria using antibodies to mercury reductases]. / Izuchenie gorizontal'nogo perenosa genov ustoichivosti k rtuti v prirodnykh populiatsiiakh bakterii s pomoshch'iu antitel k rtut'-reduktazam.

Mercury resistant soil and intestinal bacteria were isolated from different mercury deposit areas of the USSR. Mercury reductases from all gram negative bacteria studied (Pseudomonas, Acinetobacter and Enterobacterial species) with a single exception (Flavobacterium sp.) were immunologically cross reactive. Two immunological types of mercury reductases were found among gram positive bacteria (Bacillus, Staphylococcus and Coryneform species). Further subdivisions were done by "spur" formation tests. Despite considerable diversity of mercury reductases revealed in this study, we found several strains which belonged to distant genera but contained immunologically indistinguishable enzymes. This suggested that the horizontal spread of the corresponding genes occurred in these genera in relatively recent time.

[Mutation slowing down the degradation of the beta beta'-subunits of Escherichia coli RNA-polymerase]. / Mutatsiia, zamedliaiushchaia degradatsiiu beta beta'-sub"edinits RNK-polimerazy Escherichia coli.

The rpoC1 ts mutation affecting the RNA polymerase beta' subunit accelerates synthesis of RNA polymerase beta beta' subunits at 42 degrees C, while the surplus amount of subunits degrades in an hour's time. In a Ts strain with two RNA polymerase mutations, rpoC1 and rpoB251, we obtained a ts+ reversion designated opr24 which slows down degradation of surplus beta beta' subunits. The slowing down of degradation and the resulting accumulation of beta beta' subunits does not affect the kinetics of beta beta' subunit synthesis after the transfer to 42 degrees C. The effects of the opr24 are allele non-specific. The mutation also slows down degradation of beta' subunit and the amber fragment of beta subunit in the strain with subunit amber mutation rpoB22. Besides, the opr24 mutation reduces proteolysis of anomalous proteins containing canavanine. The opr24 mutation has been mapped between 17 and 21 minutes on the Escherichia coli map.

[Mutation affecting the rate of RNA-polymerase beta beta'-subunit synthesis in Escherichia coli]. / Issledovanie mutatsii, vliiaiushchei na skorost' sinteza beta beta'-sub"edinits RNK-polimerazy Escherichia coli.

As shown previously, rpoC1 temperature sensitive mutation affecting RNA polymerase beta' subunit, results in acceleration of beta beta' subunit synthesis at 42 degrees C. Also, it leads to the change in RNA polymerase sedimentation coefficient and to the reduction of RNA polymerase activity in vitro. According to the existing hypotheses, these properties of a mutant enzyme may be the cause of acceleration of synthesis of RNA polymerase in vitro. The opr1 mutation was found among Ts+ revertants of the Ts double mutant carrying rpoC1 and rif-r rpoB251 mutations. Reduction of the rate of beta beta' subunit synthesis caused by the opr1 mutation, is related to the structural changes of RNA polymerase itself. It has been shown, however, that the low activity in vitro and the altered sedimentation coefficient of the enzyme are not responsible for the accelerated synthesis of beta beta' subunits at 42 degrees C in the RpoC1 strains. Opr1 is a dominant mutation and it is located in the rpoBC region of the genetic map of Escherichia coli chromosome.

[Cold-sensitive mutation in the beta-subunit of Escherichia coli RNA polymerase affecting the opening of promoters]. / Knolodochuvstvitel'naia mutatsiia V beta-subdedinntse RNK-polimerazy Escherichia coli, vliiaiushchaia na otkryvanie promotorov.

A cold-sensitive mutation in Escherichia coli, affecting the beta-subunit of RNA polymerase and causing an increase in the temperature of promoter opening on T2 phage DNA, was obtained. The mutation also affects the stages preceding promoter opening by increasing the dissociation rate of RNA polymerase--DNA closed complexes. The affinity of RNA polymerase to T2- and lambda-DNA is differently changed by the mutation. The relative efficiency of transcription of these two templates is also changed. These results suggest a participation of the beta-subunit of RNA polymerase in the interaction with promoters.

[Effect of several factors on synthesis of RNA-polymerase subunits by Escherichia coli K12]. / Vliianie nekotorykh faktorov na sintez sub''edinite RNK-polimerazy Escherichia coli K12.

In merodiploid cells containing a double dose of structural genes of RNA polymerase subunits--rpoB and rpoC--the rate of synthesis of beta- and beta'-subunits is 2 times higher than in haploid cells. Missense mutation rpoC1 (tsX) in the beta'-polypeptide gene accelerates the synthesis of both beta- and beta'-subunits, particularly at a nonpermissive temperature. When rpoB-rpoC operon containing mutation rpoC1 is duplicated no dose effect of these genes is observed. In the heterozygous state mutation rpoC1 produces almost no accelerating effect on the synthesis of RNA polymerase subunits i. e. is recessive with respect to the wild allele of rpoC. In the presence of rifampicin the synthesis of RNA polymerase subunits in a sensitive wild-type strain is stimulated 6-fold, the same effect is observed with cells carrying mutation rpoC1, the latter, however, itself accelerates the synthesis of these subunits 3-fold. Thus the effects of rifampicin and the mutation are synergistic indicating that these factors act independently. Similar data have also been obtained with rifampicin-treated cells of rpoB22 amber-mutant. In UV-irradiated cells, amino acid incorporation into beta- and beta'-subunits declines more rapidly than into the total protein. When either irradiated or non-irradiated cells are infected with a transducing phage lambdarifd-47 which carries rpoB gene, the synthesis of beta-proceeds at a higher rate. Irradiation of bacteria before the infection (500 erg/mm2) results in 6.5-fold acceleration of the synthesis induced by subsequent infection with lambdarifd-47 as compared to non-infected non-irradiated cells; the fraction of newly formed beta-polypeptide with respect to total protein grows 20-fold in this case. The data are considered with regard to the possible mechanisms of regulation of synthesis of RNA polymerase subunits.

[Sex factor F of Escherichia coli K12 and its participation in mobilizing bacterial chromosomes]. / Polovoi faktor F Escherichia coli K12 i ego uchatie v mobilizatsii bakterial'noi khromosomy.

The structural and functional organization of F-factor reviewed and the physical map of F DNA, supplemented with a list of genetic markers, is presented. The DNA transfer during the conjugation is considered and especial attention is given to F-gene functions involved in this process. The special sequences of F DNA, homologous to resident insertion sequences in bacterial DNA are described and its participation in plasmido-chromosomal recombinant events both dependent and independent on recA function is discussed. The mechanism for chromosome mobilization by F-Factor are reviewed. A possibility of chromosome transfer without F DNA insertion is considered. In a latter case it proposed that spontaneous single-strand breaks may serve as the origins for initiation of chromosomal transfer.