Identification of a new exon of the brain microtubule-associated protein 2.

The 5'-region of the transcripts encoding the HMW-(MAP2b) and LMW-(MAP2c) microtubule associated proteins in the brain was amplified by RT-PCR. The sequencing of cloned PCR fragments allowed to identify a new variant of brain HMW-MAP2 which contained, compared to MAP2b, an insertion of 246 bp located downstream the 5'-junction between MAP2b and MAP2c and that does not alter the open reading frame of MAP2b. The number of amino acid residues encoded by this insertion increases the molecular weight by 8.5 kDa i.e. corresponds to the difference in apparent size between MAP2a and MAP2b. A LMW-MAP2 PCR amplification product containing this insertion has been also identified. Genomic Southern blot analysis confirmed that this region belongs to the MAP2 gene and is located on a single exon.