Correct Post‐Translational Modification and Stable Vacuolar Accumulation of Phytohemagglutinin Engineered to Contain Multiple Methionine Residues

Most legume seed storage proteins are deficient in sulfur amino acids. In this study, we demonstrate that replacing specific amino acid residues of a seed protein with methionine residues at positions known to be occupied by methionine residues in homologous proteins, is an effective strategy to create methionine‐enriched seed proteins. Mutant phytohemagglutinin polypeptides with three or four methionine residues were found to undergo correct post‐translational modifications in transformed cultured tobacco cells and to accumulate stably in the protein storage vacuoles of transgenic tobacco seeds.