IDENTIFICATION OF A NOVEL PROTEIN-KINASE-A ANCHORING PROTEIN THAT BINDS BOTH TYPE-I AND TYPE-II REGULATORY SUBUNITS

Compartmentalization of cAMP-dependent protein kinase is achieved in p art by interaction with A-kinase anchoring proteins (AKAPs), All of th e anchoring proteins identified previously target the kinase by tether ing the type II regulatory subunit, Here we report the cloning and cha racterization of a novel anchoring protein, D-AKAP1, that interacts wi th the N terminus of both type I and type II regulatory subunits, A no vel cDNA encoding a 125-amino acid fragment of D-AKAP1 was isolated fr om a two-hybrid screen and shown to interact specifically with the typ e I regulatory subunit, Although a single message of 3.8 kilobase pair s was detected for D-AKAP1 in all embryonic stages and in most adult t issues, cDNA cloning revealed the possibility of at least four splice variants, All four isoforms contain a core of 526 amino acids, which i ncludes the R binding fragment, and may be expressed in a tissue-speci fic manner, This core sequence was homologous to S-AKAP84, including a mitochondrial signal sequence near the amino terminus (Lin, R, Y., Mo ss, S, B,, and Rubin, C, S, (1995) J, Biol, Chem. 270, 27804-27811), D -AKAP1 and the type I regulatory subunit appeared to have overlapping expression patterns in muscle and olfactory epithelium by in situ hybr idization, These results raise a novel possibility that the type I reg ulatory subunit may be anchored via anchoring proteins.