PHOSPHORYLATION OF THE REGULATORY SUBUNIT OF TYPE-II-BETA CAMP-DEPENDENT PROTEIN-KINASE BY CYCLIN B/P34(CDC2) KINASE IMPAIRS ITS BINDING TO MICROTUBULE-ASSOCIATED PROTEIN-2

Subcellular localization of type II cAMP-dependent protein kinase is determined by the interactions of the regulatory subunit (RII) with specific RII-anchoring proteins. By using truncated NH2-terminal RIIbeta fusion proteins expressed in Escherichia coli and the mitotic protein kinase p34cdc2 isolated from HeLa cells or starfish oocytes, we investigated the in vitro phosphorylation of RIIbeta by these kinases. The putative site for phosphorylation by the mitotic kinases is Thr-69 in the NH2-terminal domain of RIIbeta. This phosphorylation site matches the consensus sequence X(T/S)PX(K/R) for p34cdc2 recognition and belongs to a well-conserved sequence found in all RIIbeta sequences known to date. In contrast to phosphorylation by casein kinase II or the cAMP-dependent protein kinase catalytic subunit, phosphorylation of RIIbeta by mitotic kinases impaired its interaction with a well-known RII-anchoring protein, the neuronal microtubule-associated protein 2. The potential regulatory significance of the phosphorylation of this site on the interaction with microtubule-associated protein 2 and other RII-anchoring proteins and the physiological relevance of this cyclin B/p34cdc2 kinase-catalyzed modification of RIIbeta (or phosphorylation by other proline-directed protein kinases) are discussed.