Using a yeast two-hybrid system, we isolated eight cDNA clones which interacted with BH-protocadherin-c (BH-Pcdh-c) from the human brain cDNA library. One clone encoded protein phosphatase type 1 isoform α (PP1α) and another two PP1α2. PP1α was co-immunoprecipitated from the extract of a gastric adenocarcinoma cell line MKN-28 with anti-BH-Pcdh-c antibody. PP1α activity towards glycogen phosphorylase was inhibited by the intracellular domain of BH-Pcdh-c. Inhibition of the phosphatase required more than the minimal domain of BH-Pcdh-c which could associate with PP1α. In situ hybridization revealed that BH-Pcdh-c mRNA was predominantly expressed in cerebral cortex neurons in the adult mouse brain. Copyright (C) 1999 Federation of European Biochemical Societies.