The effect of plasmid pKM101 on umuDC gene function enhancing precise excision of transposons.

Mutation in the thr gene with the highest UV-induced reversion frequency has been chosen from a number of mutations arisen from insertion of transposon Tn10 into the umuDC- Salmonella typhimurium. This mutation has been transferred by transduction into the Salmonella strain carrying E. coli umuDC+ genes. umuDC- and umuDC+ Salmonella strains, bearing the same insertion mutation, were used to study the effect of umuDC genes and of plasmid pKM101 on spontaneous and UV-induced precise excision of Tn10. This process, like point mutagenesis, is shown to be umuDC-stimulated. Plasmid pKM101 eliminates the effect of umuDC+ genes on UV-induced Tn10 precise excision, in contrast to its effect on point mutagenesis, and does not enhance spontaneous precise excision of Tn10.