Expression of human dihydrofolate reductase cDNA and its induction by chloramphenicol in Bacillus subtilis

A bifunctional plasmid (pMP358) able to replicate and to express cloned human dihydrofolate reductase cDNA (cDHFR) in both Escherichia coli and Bacillus subtilis was constructed. The expression of cDHFR in B. subtilis was the result of a deletion that placed the cDNA fragment under the control of the chloramphenicol acetyltransferase (CAT) gene promoter of Staphylococcus aureus plasmid pC194. By sequence analysis of plasmid pMP358, we observed a gene fusion occurring between the cDHFR and the 32nd codon of the CAT gene. We report that such a "hybrid" gene is able to direct the synthesis of a 25-kDal "hybrid" protein, which was found to be inducible by supplementing B. subtilis cells with sublethal doses of chloramphenicol.