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 (By similarity). 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. Interacts with RB1. Interacts with CD226. Interacts with SYMPK. Predominantly in the cytosol. Belongs to the SSU72 phosphatase family.