Involved in the first step of essential amino acids lysine, threonine, methionine and isoleucine synthesis via the aspartate-family pathway. ATP + L-aspartate = 4-phospho-L-aspartate + ADP Inhibited by S-adenosyl-L-methionine (SAM) and lysine in a synergistic manner. No inhibition by threonine, leucine or SAM alone, and no activation or inhibition by alanine, cysteine, isoleucine, serine, valine, methionine, glutamine, asparagine, glutamic acid or arginine. K(cat) is 23.4/sec. Amino-acid biosynthesis; L-lysine biosynthesis via DAP pathway; (S)-tetrahydrodipicolinate from L-aspartate: step 1/4. Amino-acid biosynthesis; L-methionine biosynthesis via de novo pathway; L-homoserine from L-aspartate: step 1/3. Amino-acid biosynthesis; L-threonine biosynthesis; L-threonine from L-aspartate: step 1/5. Homodimer. Only one ACT domain (ACT1) is implicated in effector binding. Belongs to the aspartokinase family.