Plasmid pIMI38--the pBR322 derivative with increased stability in E. coli cells.

Plasmid pIM138 which had been characterized by the higher resistance of its DNA replication to the action of clorobiocin in comparison with the progenitor plasmid, was tested for its stability in host cells in the absence of the antibiotic. Growing without selective pressure, pIM138 was better maintained in cells than pBR322. The stability in the presence and in the absence of clorobiocin can be unanimously assigned to the plasmid itself, but some influence of host cells cannot be excluded.

Transfer of plasmids from Escherichia coli and Pseudomonas aeruginosa to methylotrophic bacteria and their detection in the new hosts.

Several plasmids of incompatibility group P were transferred from Escherichia coli and Pseudomonas aeruginosa strains to Methylophilus methylotrophus and two other methylotrophs to test their recipient ability. The presence of plasmids in transconjugants was confirmed by electrophoretic analysis. Optimal conditions for detection of plasmid DNA in the strains tested based on alkaline lysis of cells at elevated temperature were established.

Isolation and characterization of mutants of the RP4 plasmid coding for increased resistance to ampicillin.

E. coli strain J53(RP4) was mutagenized with ethyl methanesulfonate and N-methyl-N'-nitro-N-nitrosoguanidine. Clones showing a two-to threefold increase in resistance to ampicillin were produced.

Stability of the hybrid plasmid pIM138 and its curing by some eliminating agents.

Hybrid plasmid pIM138 was constructed by insertion of a chromosomal fragment with the threonine operon from Escherichia coli into the pBR322 vector. Molar mass of pIM138 was 2.8 Mg/mol.

Curing effect of clorobiocin on Escherichia coli plasmids.

Clorobiocin, an inhibitor of the gyrB subunit of DNA gyrase, was used for the curing of some Escherichia coli plasmids. Of the plasmids studied, ampicillin resistant R28K and a miniplasmid derived from R1drd-19 were effectively eliminated. We also succeeded in eliminating the ColA factor from E.