Technical Abstract: Soybean, Glycine max, is a major crop in the United States and world wide. The level of the essential amino acid, methionine, is low in soybean meal, therefore increasing the level of methionine in soybean through breeding and through molecular techniques could decrease farmer and consumer costs. The enzyme, aspartokinase, is the first enzyme in the complex biochemical pathway leading to methionine synthesis. The several isoforms are regulated by lysine and threonine, end products of the pathway. Previously, we reported the cloning of a cDNA encoding the threonine sensitive isoform which also contains homoserine dehydrogenase activity. Now we have cloned a cDNA encoding a monofunctional aspartokinase which we believe represents the lysine isoform. The gene is expressed more in light grown tissues than in dark grown tissues, indicating regulation by light. The mRNA is approximately 2.25 kb. This information is important to scientists and breeders interested in modifying aspartokinase to increase the synthesis of methionine in soybean and other crops.