Mechanisms of synthesis and processing of four genotypic variants of phaseolin.

Newly-synthesized (unprocessed) phaseolin in all cultivars is composed of three major components. These differ between cultivars, both in charge and Mr. The processing of these precursors is highly conserved and consists of the co-translational cleavage of a signal peptide, two glycosylation steps in the endoplasmic reticulum and a further modification inside the protein bodies to give the mature form. Some of the molecular heterogeneity of each phaseolin banding type is due to a different extent of glycosylation of its polypeptide components.