Abstract
To assess whether removal of UV-induced cyclobutane pyrimidine dimers (CPDs) occurs with equal efficiency at different stages of the cell cycle in a cell cycle-regulated gene, we have analyzed repair of CPDs, following a single dose of UV, in normal human fibroblasts that were synchronized in either G(0) or S phase. Based on a single nucleotide resolution analysis, we established a detailed map of DNA repair rates along the promoter region and the transcription initiation area of the human CDC2 gene. The promoter of this gene is covered by an array of sequence-specific transcription factors located between nt -280 and -9 relative to the major transcription start site. In both quiescent and S phase-synchronized fibroblasts the majority of these sequences were poorly repaired even after 24 h, probably as a result of the constitutive binding of transcription factors throughout the cell cycle. A domain of fast repair was found at sequences surrounding the transcription initiation site and continuing downstream for approximately 80 nt. CPD removal from this domain was preferential in both quiescent and proliferating fibroblasts, despite lower levels of global genome repair and a lack of CDC2 transcription in quiescent cells. We suggest that sequences involved in transcription initiation may be book-marked for efficient repair throughout the cell cycle, even when the gene is temporarily not expressed.