Tau is a family of six isoforms, derived from a single gene by alternative mRNA splicing1. They vary in size from 352 to 441 amino acids (36.8 to 45.9 kDa), and differ from one another in having three or four microtubule binding repeats (R) of 31-32 amino acids each, and two, one or none amino terminal inserts (N) of 29 amino acids each2.Reactivity: Human TAU phosphorylated at amino acid position 231 (T)