PriA mutations that affect PriA-PriC function during replication restart

In Escherichia coli, repair and restart of collapsed replication forks is t hought to be essential for cell growth. The replication restart proteins, P riA, PriB, PriC, DnaB, DnaC, DnaG, DnaT and Rep, form redundant pathways th at recognize repaired replication forks and restart them. Recognition, modu lation of specific DNA structures and loading of the replicative helicase b y the replication restart proteins, is likely to be important for replicati on restart. It has been hypothesized that PriB and PriC function with PriA in genetically separate and redundant PriA-PriB and PriA-PriC pathways. In this study, the del(priB)302 or priC303::kan mutations were used to isolate the PriA-PriB and PriA-PriC pathways genetically so that the effects of th ree priA missense mutations, priA300 (K230R), priA301 (C479Y) and priA306 ( L557P), on these pathways could be assessed. In a wild-type background, the three priA mutations had little, if any, effect on the phenotypes of UV re sistance, basal levels of SOS expression and cell viability. In the priB mu tant, priA300 and priA301 caused dramatic negative changes in the three phe notypes listed above (and others), whereas the third priA mutant allele, pr iA306, showed very little negative effect. In the priC mutant, all three pr iA mutations behaved similarly, producing little, if any, changes in phenot ypes. We conclude that priA300 and priA301 mostly affect the PriA-PriC path way and do so more than priA306. We suggest that PriA's helicase activity i s important for the PriA-PriC pathway of replication restart.