Cell cycle-independent removal of UV-induced pyrimidine dimers from the promoter and the transcription initiation domain of the human CDC2 gene

To assess whether removal of UV-induced cyclobutane pyrimidine dimers (CPDs ) occurs with equal efficiency at different stages of the cell cycle in a c ell cycle-regulated gene, we have analyzed repair of CPDs, following a sing le 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 esta blished a detailed map of DNA repair rates along the promoter region and th e transcription initiation area of the human CDC2 gene. The promoter of thi s gene is covered by an array of sequence-specific transcription factors lo cated between nt -280 and -9 relative to the major transcription start site . In both quiescent and S phase-synchronized fibroblasts the majority of th ese sequences were poorly repaired even after 24 h, probably as a result of the constitutive binding of transcription factors throughout the cell cycl e. A domain of fast repair was found at sequences surrounding the transcrip tion initiation site and continuing downstream for similar to 80 nt, CPD re moval from this domain was preferential in both quiescent and proliferating fibroblasts, despite lower levels of global genome repair and a lack of CD C2 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.