Inducible error-prone repair in Escherichia coli.

A hypothesis that ultraviolet-induced mutagenesis arises from the induction of an error-prone mode of postreplication repair that requires the exrA+ recA+ genotype has been tested with alkaline sucrose gradient centrifugation coupled with assays of fixation determined by loss of photoreversibility. The inhibitor of protein synthesis, chloramphenicol, added before irradiation, prevented a small amount of postreplication repair and completely eliminated mutation fixation in E. coli WP2s uvrA. However, chloramphenicol did not affect strand joining: (a) in uvrA bacteria allowed 20 min of growth between irradiation and antibiotic treatment; (b) in nonmutable uvrA exrA bacteria; and (c) in uvrA tif bacteria grown at 42 degrees for 70 min before irradiation. These observations indicate that an inducible product is involved in a fraction of postreplication repair and is responsible for induced mutagenesis.