Resolving the subtle details of human DNA alkyltransferase lesion search and repair mechanism by single-molecule studies.

SignificanceWe directly visualize DNA translocation and lesion recognition by the O 6 -alkylguanine DNA alkyltransferase (AGT). Our data show bidirectional movement of AGT monomers and clusters on undamaged DNA that depended on Zn 2+ occupancy of AGT. A role of cooperative AGT clusters in enhancing lesion search efficiencies by AGT has previously been proposed. Surprisingly, our data show no enhancement of DNA translocation speed by AGT cluster formation, suggesting that AGT clusters may serve a different role in AGT function. Our data support preferential cluster formation by AGT at alkyl lesions, suggesting a role of these clusters in stabilizing lesion-bound complexes. From our data, we derive a new model for the lesion search and repair mechanism of AGT.