Comparison of the resA1 and polA1 mutations in isogenic strains of Escherichia coli K-12.

Strains carrying either the polA1 or resA1 mutation are deficient in DNA polymerase I, and the polA1 and resA1 mutations do not complement in merozygotes. The effect of these mutations in otherwise identical genetic backgrounds was studied: after ultraviolet irradiation both strains degrade their DNA more rapidly and more extensively than the wild-type strains. However, after X-ray irradiation the resA1 strain shows little DNA breakdown and repairs its single-strand breaks. In contrast, the polA1 strain degrades its DNA extensively, and single-strand breaks are not repaired. Moreover, the resA1 strain is capable of supporting the growth of a red(-) bacteriophage lambda, whereas the polA1 strain is not.