The complex of PP1 and its regulatory subunit PPP1R10 (also known as PNUTS) functions as part of the cleavage and polyadenylation complex (CPA). Two catalytic subunits of PP1 (PPP1CA and PPP1CB) co-immunoprecipitate (co-IP) with the CPA complex (Shi et al. 2009: co-IP of PPP1CA and PPP1CB shown; Erickson et al. 2025: co-IP of PPP1CA with PPP1R10 in the context of RNA Pol II association). The PP1:PPP1R10 complex stimulates transcription termination by the paused RNA polymerase II (RNA Pol II), a necessary pre-requisite in 3' end processing, by dephosphorylating serine residue 5 (Ser5) of the heptapeptide repeats in the C-terminal domain of the RNA Pol II subunit POLR2A (Washington et al. 2002: human PP1 and recombinant mouse CTD of POLR2A were used; Lee et al. 2010: human PP1:PPP1R10 complex and mouse CTD of POLR2A were used; Ciurciu et al. 2013: Drosophila proteins were used; Erickson et al. 2025: human proteins were used). PP1:PPP1R10 complex has also been reported to dephosphorylate other proteins associated with the RNA Pol II, such as the transcription elongation factor SUPT5H (also known as Spt5) (Cortazar et al. 2019). The association of the PP1:PPP1R10 complex with the restrictor complex, ZC3H4:WDR82, may contribute to PP1-mediated termination of transcription (Erickson et al. 2025).