RPRD1B, together with RPRD1A, can accompany RNAP II from promoter regions to 3'-untranslated regions during transcription in vivo, predominantly interact with phosphorylated RNAP II, and can reduce CTD S5- and S7-phosphorylated RNAP II at target gene promoters. RNA polymerase II C-terminal domain (CTD) phosphorylation is important for various transcription-related processes. RPRD1B is a transcriptional regulator which enhances expression of CCND1. It 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.
