PP1-GAMMA-2, A TESTIS-SPECIFIC PROTEIN-SERINE THREONINE-PHOSPHATASE TYPE-1 CATALYTIC SUBUNIT, IS ASSOCIATED WITH A PROTEIN HAVING HIGH SEQUENCE HOMOLOGY WITH THE 78-KDA GLUCOSE-REGULATED PROTEIN, A MEMBER OF THE 70-KDA HEAT-SHOCK PROTEIN FAMILY

Protein phosphatase 1gamma2 (PP1gamma2) is a testis-specific isotype of the protein-serine/threonine-phosphatase type 1 catalytic subunit. Three native forms of PP1gamma2 were detected in a crude fraction of rat testis by electrophoresis in a nondenaturing polyacrylamide gel. We purified a major native form of PP1gamma2 to homogeneity by successive column chromatography on Mono Q-Sepharose, EAH-agarose, protamineagarose, and G3000SW and by electrophoresis in a nondenaturing polyacrylamide gel. The G3000SW-purified PP1gamma2 native form had an apparent molecular mass of 170 kDa. The purified holoenzyme from nondenaturing polyacrylamide gel was composed of the catalytic subunit and two noncatalytic subunits, of 78 kDa and 55 kDa. Partial amino acid sequence analysis of the 78-kDa protein suggested that it is the 78-kDa glucose-regulated protein, a member of the 70-kDa heat shock protein family. The 78-kDa protein may possibly function as a chaperone or by confirming substrate specificity of PP1gamma2.