Interacts with phosphorylated C-terminal heptapeptide repeat domain (CTD) of the largest RNA polymerase II subunit POLR2A, and participates in dephosphorylation of the CTD by RPAP2. Transcriptional regulator which enhances expression of CCND1. Promotes binding of RNA polymerase II to the CCDN1 promoter and to the termination region before the poly-A site but decreases its binding after the poly-A site. Prevents RNA polymerase II from reading through the 3' end termination site and may allow it to be recruited back to the promoter through promotion of the formation of a chromatin loop. Also enhances the transcription of a number of other cell cycle-related genes including CDK2, CDK4, CDK6 and cyclin-E but not CDKN1A, CDKN1B or cyclin-A. Promotes cell proliferation. Homodimer. May form a heterodimer with RPRD1A. Associates with RPAP2. Associates with the RNA polymerase II complex. Widely expressed in the adult with highest levels in liver, colon, prostate and uterus and lowest levels in heart and kidney. Not detected in rectum. Highly expressed during early embryonic development (at protein level). Low levels detected in the adult. Belongs to the UPF0400 (RTT103) family.