The microtubule-associated proteins (MAPs) coassemble with tubulin into microtubules in vitro. Microtubule-associated protein tau appears to be enriched in axons. Tau are composed of 352 to 441 amino acids. The isoforms differ from each other by the presence or absence of 29-amino acid or 58-amino acid inserts located in the N terminus and a 31-amino repeat located in the C terminus. tau is important in establishing and maintaining neuronal morphology and is a major component of the neurofibrillary tangles (NFTs) characteristic of Alzheimer's brain. Microtubule-associated protein tau (MTBT1) is mapped to chromosome 17q21.