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

Abstract

Genetic analysis of histidine independent (His⁴) revertants induced by ultraviolet light in the his-4 E. coli strain AB1157 was carried out: 83% 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 λpsu 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 tRNA ₁ ^Gln by a CAA→TAA change in the tRNA gene while 31% affected tRNA ₂ ^Gln by TAG→TAA change. Although we were unable to deduce the base substitution of the remaining 13%, the results indicated that most of the suppressor mutations are caused by a 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 nonparing DNA lesions.