Sequence of amyloid fibril protein. The carboxyl-terminal portion of the fibrinogen Aα-chain amino acid and gene sequence are shown. The abnormal amino acid sequence resulting from deletion of the second nucleotide in the codon for Val522 (delT4897) is shown in the boxed area. The arrows indicate the peptides used to determine the amino acid sequence of the amyloid protein. The parentheses within the arrow for intact protein indicate residues tentatively identified, and dots at the end indicate that the protein continued but was not sequenced further. Peptides labeled with T were isolated from HPLC fractionation of a trypsin digest of the subunit protein (Fig 2). Dashed arrows indicate peptides recovered at ≤5% the molar amount of the other peptides.