Microtubule-associated protein tau. Identification of a novel peptide from bovine brain

The microtubule-associated protein tau isolated from bovine brain was cleaved with CNBr and the 3 largest peptides of approx. 21, 19 and 18 kDa were obtained. Dephosphorylation of the CNBr digest of tau with alkaline phosphatase changed the electrophoretic mobility of these peptides to 19, 18 and 17 kDa. Amino acid sequencing of the total CNBr digest of tau revealed at least 3 sequences, two of which were highly homologous to previously published mouse and human tau sequences derived from cDNAs. A third amino acid sequence of 17 residues with heterogeneity at position 11 showed no homology with the cDNA-derived tau sequences. These studies suggest that the amino acid sequences of mammalian tau predicted from their cDNAs might be incomplete.