Identification and functional analysis of a CDE/CHR element in the POLD1 promoter.

DNA polymerase delta is encoded by the POLD1 gene, the transcription of which is strictly cell cycle-dependent. However, the means by which POLD1 transcription is regulated by the cell cycle mechanism is currently unknown. We discovered a novel element in the POLD1 promoter known as a CDE(cell cycle-dependent element)/CHR(cell cycle gene homology region) element. A series of luciferase reporter constructs containing various POLD1 promoter mutations were used to investigate the role of the CDE/CHR element in POLD1 transcription. When the CDE/CHR element was mutated, the promoter activity was up-regulated, and the cell-cycle related factors E2F1 and p21 stopped regulating the promoter. Furthermore, cell cycle-dependent changes in the promoter activity required the integrative CDE/CHR element. Electrophoretic mobility shift assay (EMSA) revealed the presence of at least three types of DNA/protein complexes binding to the CDE/CHR element. Our findings provide strong evidence that the CDE/CHR-like sequence is an active functional element in the POLD1 promoter, which is important for the cell cycle regulation of the POLD1 gene.