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.