Acts as a transcriptional repressor (PubMed:20797634). Represses cAMP-responsive element (CRE)-mediated transcriptional activation (PubMed:21706167). In addition, has a role in translesion DNA synthesis. Requires for UV-inducible RAD18 loading, PCNA monoubiquitination, POLH recruitment to replication factories and efficient translesion DNA synthesis (PubMed:24657165). Plays a key role in the transcriptional regulation of T lymphocyte development (By similarity).