Protein phosphatase that displays CTD phosphatase activity and regulates transcription of snRNA genes. Recognizes and binds phosphorylated ‘Ser-7’ of the C-terminal heptapeptide repeat domain (CTD) of the largest RNA polymerase II subunit POLR2A, and mediates dephosphorylation of ‘Ser-5’ of the CTD, thereby promoting transcription of snRNA genes (PubMed:17643375, PubMed:22137580, PubMed:24997600). Downstream of EIF2AK3/PERK, dephosphorylates ERN1, a sensor for the endoplasmic reticulum unfolded protein response (UPR), to abort failed ER-stress adaptation and trigger apoptosis (PubMed:30118681).