(A) Coomassie-stained SDS–PAGE gel of tubulin after subtilisin digestion for 0 or 5 min. Boxes indicate the bands SF1 (black), SF4 (blue), and SF5 (red) that were excised and analyzed by mass spectrometry. (B) Amino acid sequence of residues 393–445 of Sus scrofa TUBB2B shown for reference alongside peptides identified in the SF5 band. We were not able to identify peptides corresponding to the β-tubulin carboxy termini in any of the other bands analyzed, likely because of high levels of heterogeneity introduced by posttranslational modifications. (C) Amino acid sequence of residues 403–451 of Sus scrofa TUBA1B shown for reference alongside peptides identified in the SF1 (black), SF4 (blue), and SF5 (red) bands.