Protein phosphatase that catalyzes the dephosphorylation of the C-terminal domain of RNA polymerase II. Plays a role in RNA processing and termination. Plays a role in pre-mRNA polyadenylation via its interaction with SYMPK. H2O + O-phospho-L-seryl-[protein] = L-seryl-[protein] + phosphate H2O + O-phospho-L-threonyl-[protein] = L-threonyl-[protein] + phosphate Interacts with GTF2B (via C-terminus); this interaction is inhibited by SYMPK (PubMed:15659578, PubMed:29158257). Interacts with RB1 (PubMed:15659578). Interacts with CD226 (PubMed:15659578). Interacts with SYMPK (PubMed:20861839, PubMed:23070812). Predominantly in the cytosol. Belongs to the SSU72 phosphatase family.