The details of the organization and structure of the genes encoding storage proteins and the nature of the DNA sequences regulating their expression have been worked out. This has made it possible to manipulate these genes in order to improve the nutritional value of seeds. There have been a variety of genetic approaches improving nutritional quality of seeds. Early attempts concentrated on screening of existing cultivars for unusual amino acid compositions. The low content of methionine in phaseolin, the absence of sulfur amino acids in phytohemaglutinin and its antimetabolic properties greatly contribute to the lowering of the nutritional value of the bean seeds. The low lysine content is primarily responsible for the poor nutritional quality of high prolamine-containing cereals. The prolamines of most cereals are complex mixtures of polypeptides that occur in protein bodies. Some of these proteins can be cross-linked by disulfide bonds, thus forming high-molecular-weight complexes.