Regulator of type 1 phosphatases which maintains protein phosphatase activity under strict control. Regulates the nuclear localization of type 1 phosphatase GLC7 and SDS22, and is involved in the regulation of mRNA 3'-end processing. May also regulate the activity of type 1 phosphatase PPZ1 (By similarity). Interacts with GLC7, PPZ1 and SDS22. Belongs to the YPI1 family.