Replicative Helicase Assists DNA Polymerase in Bypassing a Lesion

Abstract

Unrepaired DNA lesions can inhibit replication fork progression, leading to cell death or genomic instability. Cells and viruses have evolved to possess mechanisms whereby DNA lesions could be tolerated and bypassed. A lesion may be bypassed via replication fork reversal or recruitment of a translesion polymerase. However, less is known about whether and how a replisome directly bypasses a lesion. Here, using single-molecule methods, we investigate the effect of a cis-syn TT dimer lesion in the leading strand of a DNA template. We found that T7 DNA polymerase (DNAP) on its own was incapable of lesion bypass, consistent with findings from previous biochemical studies. Surprisingly, in the presence of T7 helicase, DNAP bypassed the lesion after a transient pause during which the helicase also paused its unwinding activity. Upon lesion bypass, DNAP and the helicase concurrently resumed their activities. Our findings suggest a new lesion-bypass mechanism that is mediated via DNAP-helicase interactions.