May be involved in the C-terminal domain of RNA polymerase II dephosphorylation, RNA processing and termination. H2O + O-phospho-L-seryl-[protein] = L-seryl-[protein] + phosphate H2O + O-phospho-L-threonyl-[protein] = L-threonyl-[protein] + phosphate Predominantly in the cytosol. Belongs to the SSU72 phosphatase family.