VARIATIONS IN IN-VIVO PHOSPHORYLATION AT THE PROLINE-RICH DOMAIN OF THE MICROTUBULE-ASSOCIATED PROTEIN-2 (MAP2) DURING RAT-BRAIN DEVELOPMENT

Microtubule-associated protein 2 (MAP2) is an in vitro substrate for M AP kinase. Part of the phosphorylation occurs at the C-terminal microt ubule-binding domain of the molecule which contains a cluster of putat ive consensus sites for MAP kinase on a proline-rich region. A peptide with the sequence RTPGTPG-TPSY, located at this region of the molecul e, is efficiently phosphorylated by MAP kinase in vitro. An antibody ( 972) raised against this non-phosphorylated peptide has been used to t est for in vivo phosphorylation at the proline-rich domain of the MAP? , molecule. The reaction of purified MAP2 with antibody 972 diminishes after in vitro phosphorylation by MAP kinase and is enhanced after in vitro dephosphorylation by alkaline phosphatase. A fraction of brain MAP2 isolated by iron-chelation affinity chromatography appears to be phosphorylated in vivo at the site recognized by antibody 972. There i s some variation in the phosphorylation of MAP2 at the proline-rich re gion throughout rat brain development. MAP2C is more highly phosphoryl ated in the developing rat brain, whereas high-molecular-mass MAP2 is more extensively phosphorylated in the adult rat brain.