Identification of O* protein by mass spectrometry. (A) MALDI TOF mass spectrum of the in-gel tryptic digest of O* band from SDS-PAGE. Peaks within 0.02 Da of the theoretical mass of whole length gpO are indicated by arrows and the corresponding peptide sequences are shown. (B) Tandem mass spectrometry of 1110.71 Da peptide. The resulting spectrum corresponds to the N-terminal peptide (residues 2–10) of gpO, AKKVSKFFR. y and b ions are indicated by arrows. (C) The resulting map of gpO protein. Black, sequence of O* protein inferred from mass spectrometric data; gray, sequence of gpO not present in O*; bold, regions of gpO for which peptides were identified; underlined, peptide sequence confirmed by tandem mass spectrometry.