Defective excision and postreplication repair of UV-damaged DNA in a recL mutant strain of E. coli K-12.

The mutation recL152 leads to a reduction of excision repair as measured by an increase in the time required to close uvrA uvrB dependent incision breaks, and by a reduction of host cell reactivation ability. Postreplication repair is also delayed when measured in a uvrB5 recL152 double mutant. Such a determination could not be made using the recL152 single mutant because the excision defect led to an accumulation of breaks in the unlabeled high molecular weight DNA to which the labeled DNA synthesized after irradiation must attach in order to achieve normal high molecular weight. Further, the recL gene product seems to be required to rejoin breaks in parental strand DNA which are generated during postreplication repair, since such gaps accumulate in a recL152 uvrB5 double mutant but not in a recL+ uvrB5 single mutant. We have noticed a striking phenotypic similarity between recL152 and polA1 and suggest that recL152 is required for full in vivo activity of DNA polymerase I.