Expression of the SOS genes of Escherichia coli in Salmonella typhimurium.

To lysogenize Salmonella typhimurium by Lambda phage, a region of 10.2 kb of Escherichia coli DNA carrying the nusA gene was cloned in a S. typhimurium strain containing a F'112 plasmid which codifies for the lamB region of E. coli. The strain of S. typhimurium obtained in this way, was lysogenized by lambda c IndO- bacteriophage harboring either a fusion between recA1 or sfiA genes of E. coli with lacZ gene. Likewise, pSE143 plasmid with a umu C::lacZ fusion was introduced in S. typhimurium. Afterwards, induction of these SOS genes was studied. Results obtained show that the basal transcription of both recA and sfiA genes of E. coli was higher in S. typhimurium than in E. coli. Nevertheless, induction of recA and sfiA genes by UV-irradiation and mitomycin C was higher in E. coli than in S. typhimurium. On the other hand, umuC gene of E. coli presents the same basal level of transcription in both E. coli and S. typhimurium species, although induction of this gene by UV-irradiation and mitomycin C was higher in S. typhimurium than in E. coli. Therefore, the plasmid pUA25 constructed in this work may be used to introduce, using the Lambda phage as a vector, the SOS genes of E. coli in other bacterial species which may be useful to study the relationship between their respective SOS systems.