Human RNA polymerase II-associated protein 2 (RPAP2) interacts directly with the RNA polymerase II subunit Rpb6 and participates in pre-mRNA 3'-end formation

The C-terminal domain (CTD) of the largest subunit of RNA polymerase II (Pol II) is composed of tandem repeats of the heptapeptide Tyr1-Ser2-Pro3-Thr4-Ser5-Pro6-Ser7. The CTD of Pol II undergoes reversible phosphorylation during the transcription cycle, mainly at Ser2, Ser5, and Ser7. Dynamic changes in the phosphorylation patterns of the CTD are responsible for stage-specific recruitment of various factors involved in RNA processing, histone modification, and transcription elongation/termination. Human RNA polymerase II-associated protein 2 (RPAP2) was originally identified as a Pol II-associated protein and was subsequently shown to function as a novel Ser5-specific CTD phosphatase. Although a recent study suggested that RPAP2 is required for the efficient expression of small nuclear RNA genes, the role of RPAP2 in controlling the expression of protein-coding genes is unknown. Here, we demonstrate that the C-terminal region of RPAP2 interacts directly with the Pol II subunit Rpb6. Chromatin immunoprecipitation analyses of the MYC and GAPDH protein-coding genes revealed that RPAP2 occupied the coding and 3' regions. Notably, siRNA-mediated knockdown of RPAP2 caused defects in 3'-end formation of the MYC and GAPDH pre-mRNAs. These results suggest that RPAP2 controls Pol II activity through a direct interaction with Rpb6 and participates in pre-mRNA 3'-end formation.