Inhibitor subunit of the major nuclear protein phosphatase-1 (PP-1). It has RNA-binding activity but does not cleave RNA and may target PP-1 to RNA-associated substrates. May also be involved in pre- mRNA splicing. Binds DNA and might act as a transcriptional repressor. Seems to be required for cell proliferation. Isoform Gamma is a site-specific single-strand endoribonuclease that cleaves single strand RNA 3' to purines and pyrimidines in A+U-rich regions. It generates 5'-phosphate termini at the site of cleavage. This isoform does not inhibit PP-1. May be implicated in mRNA splicing. This is the function of ENSG00000117751 (PPP1R8, protein phosphatase 1 regulatory subunit 8).