Analysis of ultraviolet light-induced suppressor mutations in the strain of Escherichia coli K-12 AB1157: an implication for molecular mechanisms of UV mutagenesis.

Genetic analysis of histidine independent (His+) revertants induced by ultraviolet light in the his-4 E. coli strain AB1157 was carried out: 93% carried ochre (UAA) suppressor mutations and 17% carried back mutations to his+ or (intragenic?) suppressors not detectably separable from his-4. Using the specialized transducing lambda psu 2int- phage, which carries supE-supB, it was determined that 87% of the ochre suppressors mapped in the supE-supB region. We were able to deduce that 56% of these affected tRNA1Gln by a CAA leads to TAA change in the tRNA gene while 31% affected tRNA2Gln by TAG- leads to TAA change. Although we were unable to deduce the base substitution of the remaining 13%, the results indicate that most of the suppressor mutations are caused by G:C to A:T transition. These results suggest that the high incidence of supE-supB region suppressor mutation in E. coli by UV would be a reflection of the general feature of UV mutagenesis; i.e. preferential induction of G:C to A:T transition in repairing nonpairing DNA lesions. AI 05371