Expression of prokaryotic genes inserted into ColE1 and pVH51 plasmids

One of the DNA fragments obtained from EcoRI digests of guaA-transducing lambda phage DNA contains the intact bacterial guaA gene at its one end and the lambda phage R gene at the other end. This DNA fragment, named coslambda-guaA, does not contain promoter-operator regions of the gua operon and of the lambda phage R gene, coslambda-guaA DNA fragments were inserted in two different orientations into respective DNAs of EcoRI-cleaved ColE1 and pVH151 (= mini ColE1). Mitomycin C stimulated the guaA enzyme production in the cells harboring the hybrid plasmids with one coslambda-guaA DNA fragment insertion orientation (orientation I), but not the other (orientation II). The lambda-endolysin, product of the lambda phage R gene, was induced by mitomycin C treatment in orientation II, but it was not detected in orientation I. These results suggest that both ColE1 and pVH51 DNAs contain the mitomycin C-responsive promoter which allows transcription of the genes connected with these DNAs.