Specificity of UV mutagenesis in the lac promoter of M13lac hybrid phage DNA.

Abstract

The mutagenic effect of UV irradiation on Escherichia coli and its phages depends on induction of the E. coli recA+ lexA+ regulatory system (for review, see ref. 1). It is not understood how mutations result from UV damage in DNA, particularly with respect to the function(s) of proteins that may be induced in UV-irradiated cells. Misincorporation of nucleotides during DNA synthesis on template DNA containing UV-induced lesions may occur predominantly at the specific sites of damage, implying that the DNA replication apparatus in UV-irradiated cells can bypass premutational lesions. Alternatively, misincorporation may occur randomly, suggesting an altered and inaccurate DNA replication apparatus in UV-irradiated cells. To study the specificity of UV mutagenesis at the nucleotide level, we have used M13lac hybrid phage, developed by Messing and colleagues2,3 for rapid nucleotide sequencing of cloned DNA, as a forward mutation system. Nucleotide changes in a nonessential lac DNA sequence of the hybrid phage genome were determined by sequencing the DNA of mutant clones derived from UV-irradiated hybrid phage grown in UV-irradiated cells. We report here the nucleotide changes observed in the lac promoter of the mutant hybrid phage.