DNA-binding transcription regulator that regulates endothelial cell proliferation and G1/S cell-cycle progression. Specifically binds the 5'-[AT]NTNN[GT]GGCA[AGT]-3' core DNA sequence and acts by modulating expression of pRB-E2F cell-cycle target genes, including RRM1. Component of a THAP1/THAP3-HCFC1-OGT complex that is required for the regulation of the transcriptional activity of RRM1. May also have pro-apoptotic activity by potentiating both serum- withdrawal and TNF-induced apoptosis. {ECO:0000269|PubMed:12717420, ECO:0000269|PubMed:17003378, ECO:0000269|PubMed:20200153}. This is the function of THAP1 (THAP domain containing 1, ENSG00000131931).