MAPT and Alzheimer disease: PHF-core tau isolated from Pronase-treated PHF preparations from AD brain comprises a number of different fragments encompassing residues 297–391 and 264–359 from the repeats R2–R4 and repeats (R1–R3) of the 4-repeat isoform, and residues 266–391 of the 3-repeat isoform (74, 82, 83).