This is the aspartate family, since aspartate is the common precursor of lysine, methionine and threonine.

Oxaloacetate, a citric acid cycle intermediate, is the a-keto acid of aspartate, wich is so easily available by the amidation of oxaloacetate. So it's a nonessential amino acid. However, lysine, methionine and threonine are essential amino acids. The biosynthesis of these essential amino acids begin with the aspartokinase-catalyzed phosphorylation of aspartate to yield aspatil-b-P. Altough, each of these pathways is independently controlled. Escherichia coli does so via three isozymes of aspatokinase that respond differently to the three amino acids in terms both of feedback inhibition of enzyme activity and repression of enzyme synthesis. In adition, the pathway direction is controlled by feedback inhibition at the branch points by the individual amino acids.