Corn grain is an important component of feed for non-ruminant animals and food for humans. It is an excellent source of starch, but is a poor source of protein nutrition. Protein content is low, usually less than 10% of the kernel mass, and moreover, the quality of maize protein is not ideal. Maize protein is deficient in certain amino acids—lysine, tryptophan, and methionine—that are required by non-ruminant animals (including humans). To remedy these deficiencies, protein supplements are provided to create a well-balanced diet, which adds to the cost of feed and food. Genetic improvements that increase the levels of lysine, tryptophan, and methionine have been actively sought by researchers for the past fifty years. Recently, several approaches involving one or more transgenes have been successful.