Sequence analysis of recombinant and UCC–derived proMBP. The complete amino acid sequence of preproMBP28-30 is shown. N-terminal sequences were obtained as described in Materials and Methods. Underlined sequences correspond to (1) the N-terminus of purified 33-kD recombinant proMBP, (2) the N-terminus of the corresponding 18-kD intermediate form of proMBP in day-12–induced UCC, and (3) the N-terminus of 14-kD MBP in day-24–induced UCC. Amino acid residues corresponding to the leader sequence are in plain font, the propiece residues are in italics, and mature MBP residues are in bold.