Damage search mechanism of XPC-RAD23B

Abstract

Abstract In nucleotide excision repair (NER), XPC recognizes DNA lesions and provides a platform for the assembly of NER factors. However, the dynamic mechanisms by which XPC recognizes DNA defects have remained elusive. We directly visualized the motion of XPC-Rad23B on undamaged and lesion-containing DNA using high-throughput single-molecule imaging. We observed heterogeneity in one-dimensional motion of XPC-Rad23B along DNA, including diffusive, constrained, and immobile modes of mobility. Consecutive AT-tracks led to increase in proteins with constrained or immobile motion. The diffusion coefficient dramatically increased according to ionic strength, suggesting that XPC-Rad23B diffuse along DNA via hopping, allowing XPC-Rad23B to bypass protein obstacles during the search for DNA damage. We examined how XPC-Rad23B identifies cyclobutane pyrimidine dimers (CPDs) during diffusion. XPC-Rad23B makes futile attempts to bind to CPDs, consistent with low CPD recognition efficiency. In addition, XPC-Rad23B binds CPDs in biphasic states, stable long binding and unstable short binding. The low recognition efficiency and unstable binding highlight the necessity of another factor for CPD recognition. Taken together, our results provide new insight into how XPC-Rad23B can search for DNA lesions in billions of base pairs of human genome.