FIG. 4.

NER is regulated in a circadian fashion. When cellular replication machinery detects UV-induced DNA damage, NER is initiated. The clock-controlled protein XPA is a rate-limiting step of the NER process. After initiation, the damaged DNA nucleotides are removed, and DNA polymerase fills in the undamaged portion of the DNA using the complementary sequence left behind as a template. NER, nucleotide excision repair; XPA, xeroderma pigmentosum A. To see this illustration in color, the reader is referred to the web version of this article at www.liebertpub.com/ars