Effects of growth phase and repair capacity on rejoining of ethyl methanesulfonate-induced DNA breaks in Escherichia coli

Abstract

The effects of growth phase and DNA repair capacity on the production and rejoining of ethyl methanesulfonate (EMS)-induced single-strand breaks were studied in 4 strains of E. coli. DNAs from logarithmic and stationary phase cells of the DNA polymerase I deficient mutant, P 3478 polA, a recombination deficient mutant, DZ 417 recA, and from the respective parental strains, W 3110 pol + and AB 253 rec + were examined by sedimentation in alkaline sucrose gradients. In both parental strains, stationary phase cells exhibited enhanced strand rejoining. In the mutants, alkylated DNA was repaired to some extent in both growth phases, but it contained a greater proportion of small DNA fragments compared to the parental strains. Some DNA breakdown occured in all four strains but this was most extensive in stationary phase cells of the repair-deficient mutants. These results indicate that the four strains can rejoin EMS-induced DNA strand breaks with varying efficiency depending on the physiological state and the genetic capacity for repair.