MAP2A, AN ALTERNATIVELY SPLICED VARIANT OF MICROTUBULE-ASSOCIATED PROTEIN-2

MAP2, a dendritically localized microtubule-associated protein (MAP), consists of a pair of high molecular mass (280 kDa) polypeptides, MAP2 a and MAP2b, and several low molecular mass (70 kDa) proteins called M AP2c. Although MAP2b and MAP2c have been shown to arise via alternativ e splicing, it was not clear whether MAP2a is also created by alternat ive splicing or by posttranslational modification. Using epitope pepti de mapping, we have demonstrated that an element specific to MAP2a is situated at its N-terminal end. A cDNA clone from an adult rat brain l ibrary was found to contain an additional 246 nucleotides situated at the 5' end of the 9-kb MAP2 mRNA. Antibodies generated against the enc oded protein sequence recognize specifically MAP2a in rat brain homoge nates. Moreover, although MAP2a, like MAP2b, is found in dendrites and cell bodies, its temporal appearance and cell type-specific distribut ion in rat brain differs from MAP2b.