Role of plasmids in the formation of E. coli polycellular forms.

The formation of polycellular forms by E. coli strain K-12 cells containing F-like plasmids pAP22-2 and pAP42 was studied by the method of small-angle laser scattering. The efficiency and patterns of the resultant cell associations depend on genetic characteristics of the studied plasmids.

[The role of the chromosomal Thr-Leu segment of E. coli K-12 in the expression of the fin-V transfer inhibition system of the F-like plasmid pAP53].

The role E. coli K-12 cell chromosome genetic region (tis-region) in expression of fin V-transfer inhibition system of F-like plasmid pAP53 was shown. The results obtained testify the linkage of tis region and Thr-Leu chromosomal segment.

[The genetic regulatory systems of cointegrative plasmid transfer in E. coli K-12 cells].

On the basis of transfer factor pAP42 and nonconjugative plasmids pRSF2124 and pUB781, the cointegrative plasmids pAP42/pRSF2124 and pAP42/pUB781 were constructed. Complex systems of plasmid transfer inhibition (funU and finV) were detected in the structure of cointegrative plasmids.

[The genetic regulation of the conjugative properties of plasmid complex pAP18 in E. coli cells].

Natural plasmid complex pAP18 discovered in E. coli cells consists of F-like plasmid pAP18-1 (Tc, ColV) and N-like plasmid pAP18-2 (Sm) which differ in their genetic transfer. Plasmid pAP18-1 is able to inhibit transfer of plasmid pAP18-2 but not vice versa.

[Features of expression of the genetic region of plasmid pAP42, controlling the synthesis of "sex" pili and surface exclusion system in various E. coli cells].

The results of investigation of serologically--typed and nontyped E. coli cells carrying F-like derepressed plasmid pAP42 testified to the influence of genome of some bacterial hosts on the expression of plasmid genetic region determining "sex" (plasmid--specific) pili synthesis and surface exclusion system (Sfx--system). Similar changes in bacterial cells phenotype can also result from the mutational changes of this plasmid.

[Genetic region of incompatibility of the F-like plasmid pAP-18-1].

With help of molecular cloning the genetic region controlling incompatibility of plasmid pAP18-1 (Inc FXI) was localized in EcoR1-fragment f5 (3.6 MD). The genetic region of incompatibility of its derepressed mutant pAP18-1drd (Inc FVII) is situated in EcoR1-fragment f2 (7,2 MD).

[Pili determined by the tra genes of F-like plasmids].

The study of structural and functional features of plasmid-specific pili synthetized by E. coli cells under control of 27 F-like plasmids was performed. All the plasmids determined the pili of "flexible" type which were classified into 3 groups on the basis of difference in cell sensitivity to pili-specific phages f1, f2, Q.

[Systems of surface exclusion of F-like plasmids of E. coli and their genetic control].

The F-like plasmids belonging to 5 different Sfx-groups were discovered. The existence of atypical plasmids belonging to different Sfx-groups was shown. The molecular cloning of plasmid DNA fragment (3.

[Genetic organization of transfer region of F-like plasmid pAP18-1].

The results of complementation analysis of nitrosoguanidine-induced mutants of F-like drd-plasmid pAP18-1 (Tc, ColV) testified to the existence of at least 3 tra regions (tra1, tra2, tra3) and regulating locus fin V in the genome of this plasmid. By means of molecular cloning of tra2 region and locus fin V of plasmid pAP18-1drd were located in Sall-fragment f5 (3.9 MD).

[The transposon content of nonconjugated E. coli plasmids].

The search of nonconjugated plasmids in antibiotic-resistant cells of wild E. coli strains was performed and their transposon maintenance has been studied. The possibility of existence of some different nonconjugated plasmids in one bacterial cells was shown and each plasmid could carry the same transposon.

[Molecular genetic study of the changes in the incompatibility and regulation of the transfer of the F-like pAP18-1 plasmid induced by nitrosoguanidine and the Tn5 and Tn9 transposons].

Relation between induced mutations of plasmid pAP18-1 (Tc, Col) and alterations in it's restriction map was studied. Nitrosoguanidine induced mutations of transfer regulation system and incompatibility of this plasmid related with alteration in the situation of recognition sites for restrictases EcoR1 and Sal1 in map positions 42.2-4.

[Complementation analysis of derepressed mutants of F-like plasmids of Escherichia coli].

Complementation analysis of a number of conjugative transfer functions was performed in derepressed (drd) mutants of E. coli F-like plasmids. The major part of double plasmid complexes investigated has revealed the formation of complementation transfer inhibitor of Fin V-type, or less frequently--the formation of Fin U-type inhibitor.

[Genetic regulation of plasmid transfer in gram-negative bacteria].

The data are reviewed on the genetic structure and regulation of tra-genes activity controlling the conjugative transfer of F, F-like plasmids as well as the transfer of some other bacterial plasmids. The effect of the systems inhibiting the conjugational transfer (fin-systems) of F and a number of derepressed F-like plasmids has been characterized on the basis of data obtained by the authors or published data. Possible mechanisms for the systems functioning in the regulation of tra-genes activity are discussed as well as the prospects of their further study.

[Effect of transposons on the system regulating derepressed plasmid tra-genes].

The ability of standard plasmids of six Fin-groups to inhibit the functions of genes transferring derepressed F-like plasmids has been studied. It is shown that transposons incorporation into the structure of individual plasmids alters the regulatory system of plasmid tra-genes.

[Characteristics of the derepressed mutant of the F-like plasmid pAP18-1 coding for tetracycline resistance in Escherichia coli].

A transfer function derepressed mutant of the F-like plasmid pAP18-1 (Tc, ColV) was induced with the help of N-methyl-N'-nitro-N-nitrozoguanidine. The mutant plasmid pAP18-1drd belongs to the FVII incompatibility group of the F-like plasmids. The plasmid pAP18-1drd is characterized by the loss of the capacity for inhibiting the tra-genes functions of the Flac plasmid and is sensitive to the Tra-function inhibitors of the reference plasmids of the FinV and FinW groups.

[Genetic regulation of the function of E. coli plasmid pAP42 transfer genes].

Sensitivity of the genetic transfer system of F-like plasmid pAP42 marked with the transposons Tn1 and TN9 to fertility inhibitors of six reference Fin-groups was studied. It was shown that transfer function and donor-specific piliformation of the plasmid under study were inhibited by reference plasmids of FinU and FinV groups, surface exclusion by plasmids of FinU and FinQ groups. The different influence of the FinOP group plasmid on transfer functions of the marked plasmids pAP42::Tn1 and pAP42::Tn9 that is likely to be connected with the effect of incorporated transposons was determined.

[Systems regulating the tra genes of derepressed F-like plasmids].

A study was made of the ability of reference plasmids of the 6 known Fin-groups to inhibit the functions of transfer genes (tra-genes) of the 4 derepressed F-like plasmids (pAP22-2, pAP38, pAP43, pAP53). It was shown that unlike the derepressed Flac plasmid, the conjugation transfer of pAP38 and pAP53 plasmids was inhibited only by, the FinV plasmid, whereas pAP22-2 plasmids by Fin V and Fin V plasmids. The formation of donor-specific pili in case of pAP38 plasmid was inhibited by Fin Q, Fin U and Fin V plasmids, in case of pAP43 plasmid by Fin U Fin V and Fin W plasmids.

[Effect of transposons Tn1 and Tn9 on the genetic regulation system of transfer and incompatibility functions of Col-plasmid pAP19-1].

F-like pAP19-1 Col-plasmid was labeled with transposons Tn1 and Tn9 and transfer functions of its derepressed mutants were investigated. The plasmid indicated was compatible with reference plasmids of 9 F-like incompatibility groups. Thus it belongs to the new incompatibility group FX.