Protein phosphatase regulatory subunits, such as SAPS1, modulate the activity of protein phosphatase catalytic subunits by restricting substrate specificity, recruiting substrates, and determining the intracellular localization of the holoenzyme. SAPS1 is a regulatory subunit for the protein phosphatase-6 catalytic subunit (PPP6C; MIM 300141) (Stefansson and Brautigan, 2006 [PubMed 16769727]).