[Effect of plasmid R6K on expression of the temperature-sensitive mutation in gene dnaE of Escherichia coli K-12].

The multicopy, conjugative R6K plasmid is responsible for the increase in the number of temperature-resistant (Tr) clones formed by Escherichia coli K-12 E486 strain, carrying a ts mutation dnaE486 in the gene coding for DNA polymerase III. The effect observed is not due to the mutator action of R6K or a mutation in the plasmid and requires the intactness of the host recA function. Tr derivatives MG488 and MG492, isolated under non-permissive condition from the strain E486(R6K), still possess the ts allele dnaE486 in the chromosome. Both Tr derivatives are more resistant to UV-irradiation and the characterized with a different level of spontaneous and UV-induced mutagenesis as compared to the initial strain E486(R6K). The data obtained suggest that the plasmid R6K is involved in the metabolism of chromosomal DNA of the host.