MASS-SPECTROMETRIC AMINO-ACID SEQUENCING OF A MIXTURE OF SEED STORAGEPROTEINS (NAPIN) FROM BRASSICA-NAPUS, PRODUCTS OF A MULTIGENE FAMILY

The amino acid sequences of a number of closely related proteins (''na pin'') isolated from Brassica napus were determined by mass spectromet ry without prior separation into individual components. Some of these proteins correspond to those previously deduced (napA, BngNAP1, and gN a), chiefly from DNA sequences. Others were found to differ to a varyi ng extent (BngNAP1', BngNAP1A, BngNAP1B, BngNAP1C, gNa', and gNaA), Th e short chains of gNa and gNa' and of BngNAP1 and BngNAP1' differ by t he replacement of N-terminal proline by pyroglutamic acid; the long ch ains of gNaA and BngNAP1B contain a six amino acid stretch, MQGQQM, wh ich is present in gNa (according to its DNA sequence) but absent from BngNAP1 and BngNAP1C, These alternations of sequences between napin is oforms are most likely due to homologous recombination of the genetic material, but some of the changes may also be due to RNA editing, The amino acids that follow the untruncated C termini of those napin chain s for which the DNA sequences are known (napA, BngNAP1, and gNa) are a romatic amino acids, This suggests that the processing of the proprote in leading to the C termini of the two chains is due to the action of a protease that specifically cleaves a G/S-F/Y/W bond.