Protein phosphatase that associates with over 200 regulatory proteins to form highly specific holoenzymes which dephosphorylate hundreds of biological targets. Protein phosphatase 1 (PP1) is essential for cell division; and participates in the regulation of glycogen metabolism; muscle contractility and protein synthesis (By similarity). Promotes nuclear envelope reassembly by targeting nuclear membrane vesicles to chromatin at the end of mitosis. Acts by dephosphorylating membrane proteins such as lamin B receptor (lbr) to regulate the binding of membrane proteins to chromatin. {ECO:0000250; ECO:0000269|PubMed:17448463}.