[RecA-independence of the process of amplification caused by the RS-1 sequence of Vibrio cholerae]. / RecA-nezavisimost' protsessa amplifikatsii, obuslovlennogo RS1- posledovatel'nostiami kholernogo vibriona.

The processes of amplification and deamplification of a plasmid DNA segment flanked by direct repeats of RSI-sequence of Vibrio cholerae and carrying the structural genes of cholera toxin inside the recombinant plasmid in E. coli cells have been studied. These processes determined by RSI-sequences are shown to take place independent of the RecA-system of E. coli cells.

[Variants of the plasmid pAS8 delta with increased frequency of integration into Rhodopseudomonas sphaeroides chromosome--the result of IS8-element duplication]. / Varianty plazmidy pAS8-121 delta s povyshennoi chastotoi integratsiiv khromosomu Rhodopseudomonas sphaeroides--rezul'tat duplikatsii IS8-élementa.

The possible participation of IS8 and IS elements of Rhodopseudomonas sphaeroides in cointegrate formation by chromosome of the purple bacterium and plasmid pAS8-121 delta has been studied. The plasmid derivatives having deleted Tn7 have been studied. Plasmid integration into the chromosome of the purple bacterium is shown to be mediated by IS8 element of the plasmid. Plasmid derivatives having the integration potential increased for two orders were isolated by a series of intergeneric conjugational crosses during which plasmid pAS8-121 delta was transferred from Rhodopseudomonas sphaeroides (cointegrate of plasmid and chromosome) to Escherichia coli (plasmid in an autonomous state) and back to Rhodopseudomonas sphaeroides. The restriction analysis of plasmid DNA digested by Hpal and Smal restriction endonucleases has revealed the tandem duplications of IS8 in plasmids capable of integration into the chromosome of the purple bacterium with a high frequency.

[Genetic study of plasmid pVM82 which contributes to the pathogenicity of the pseudotuberculosis pathogen]. / Geneticheskoe izuchenie plazmidy pVM82, vnosiashchei vklad v patogennost' vozbuditelia psevdotuberkuleza.

The large pVM82 plasmid isolated from epidemic strains of Yersinia pseudotuberculosis includes the 25MD segment, which encodes a series of properties affecting the virulence of the bacterium. Insertion mutants of pVM82 containing transposition-defective Tn2507 with a kanamycin-resistance marker in different Hind III fragments of the 25MD segment were obtained. By recombination between two homologous pVM82 containing genetic markers in different parts, deletion derivatives of pVM82 plasmid and insertions of the plasmid segment, carrying kanamycin-resistance marker, into a chromosome were obtained. Results were obtained suggesting the presence in the plasmid 25MD segment of a transposon-like structure capable of migrating from pVM82 plasmid onto a chromosome and from a chromosome and pVM82 onto pRP1.2 plasmid of a broad host range.

[Inheritance and expression of cholera toxin genes introduced into Vibrio cholerae el tor cells in a hybrid plasmid]. / Osobennosti nasledovaniia i ékspressii genov kholernogo toksina, vvedennykh v kletki Vibrio cholerae eltor v sostave gibridnoi plazmidy.

Two replicons, pOX38 (in F-factor derivative lacking all IS elements) and pCT105 (containing cholera toxin operon cloned in pBR322) have been fused to produce recombinant plasmid, pCO109, which was then introduced into Vibrio cholerae eltor by conjugation. Restriction analysis showed pCO109 to dissociate in V. cholerae cells at a higher frequency than in Escherichia coli strains, its pOX38 component being lost, while the pCT105 component demonstrated relative stability. V. cholerae eltor RV79 (pCT105) produced 4-5 micrograms/ml of cholera toxin. Occasional insertion of cloned vctA, B operon into RV79 chromosome was also observed.

[The role of the RS1 sequence of Vibrio cholerae in the amplification of a segment of plasmid DNA carrying the tetracycline resistance gene and cholera toxin genes]. / Rol' RS1-posledovatel'nosti kholernogo vibriona v amplifikatsii segmenta plazmidnoi DNK, nesushchego gen rezistentnosti k tetratsiklinu i geny kholernogo toksina.

The clones with 4 to 30-fold increased level of tetracycline resistance (TcR) were selected from the strain of Escherichia coli K-12 carrying the pCO107 plasmid. The plasmid is the cointegrate formed from the plasmids pOX38 (F-derivative) and pCT105 (pBR322-derivative carrying the vct operon of Vibrio cholerae eltor and the RSI sequence). pCO107 contains RSI at the junctions of two plasmid genomes. Using restriction analysis and Southern blot hybridization technique it was shown that increased tetracycline resistance is accompanied by amplification of the pCT105 segment of pCO107 and depends upon the presence of direct repeats of flanking RSI. Amplification of the pCT105 also resulted in increased production of the cholerae toxin (CT).