Distinct β-clamp interactions govern the activities of the y family PolIV DNA polymerase

Abstract

The prototypic Y family DNA polymerase IV (PolIV) of Escherichia coli is involved in multiple replication-associated processes including spontaneous mutagenesis, translesion synthesis (TLS), cell fitness, survival under stressful conditions and checkpoint like functions. It interacts physically and functionally with the replisome's β processivity clamp through the canonical PolIV C-terminal peptide (CTP). A second interaction that involves a portion of the little finger (LF) domain of PolIV has been structurally described. Here we show that the LF-β interaction stabilizes the clamp-polymerase complex in vitro and is necessary for the access of PolIV to ongoing replication forks in vivo. However, in contrast to the CTP-β, the LF-β interaction is dispensable for the role of the polymerase in TLS. This discloses two independent modes of action for PolIV and, in turn, uncovers a novel way by which the cell may regulate the potentially deleterious effect of such low fidelity polymerases during replication. © 2009 Blackwell Publishing Ltd.