Ultraviolet light-induced mutation in UV-resistant, thermosensitive derivatives of lexA− strains of Escherichia coli K-12

Research paper by David W. Mount, Candace Kosel

Indexed on: 01 Jun '75Published on: 01 Jun '75Published in: Molecular & general genetics : MGG


It was shown previously that a major class of UV-resistant derivatives of lexA− strains of E. coli K-12 is defective in cell division at 42.5°. The thermosensitive mutations, judging by genetic mapping and complementation tests, are believed to be intragenic suppressor mutations that lower the activity of the diffusible product that results in the LexA− phenotype (Mount et al., 1973). Several thermosensitive derivatives have been characterized in regard to their susceptibility to mutation induction by UV at the permissive growth temperature (30°). Although the strains tested are approximately as resistant to UV as lexA+ strains, they showed a level of mutation induction that was considerably lower. By means of genetic complementation tests it was demonstrated that the low levels of UV mutagenesis in lexA− strains and their thermosensitive derivatives result from the synthesis of a diffusible product. One possible interpretation of these results is that a diffusible product in lexA− strains prevents the induction of error-prone repair. Altering the activity of this product by tsl mutations can lead to increased, but not normal, levels of error-prone repair.