ISOLATION AND CHARACTERIZATION OF PNUTS, A PUTATIVE PROTEIN PHOSPHATASE-1 NUCLEAR TARGETING SUBUNIT

Protein phosphatase 1 (PP1) is found in the cell nucleus and has been implicated in several aspects of nuclear function. We report here the cloning and initial characterization of a novel protein similar to nam ed phosphatase 1 nuclear targeting Subunit (PNUTS). This protein inter acts with PP1 in a yeast two-hybrid assay, is found in a stable comple x with PP1 in mammalian cell lysates, and exhibits a potent modulation of PP1 catalytic activity toward exogenous substrate in vitro. PNUTS is a ubiquitously expressed protein that exhibits a discreet nuclear c ompartmentalization and is colocalized with chromatin at distinct phas es during mitosis. The subcellular localization of PP1 and the activit y toward substrates involved in many aspects of cell physiology have p reviously been shown to be regulated by association with noncatalytic targeting subunits. The properties of PNUTS are consistent with its ro le as a targeting subunit for the regulation of nuclear PP1 function.