Can also synthesize a number of adenyl dinucleotides (in particular AppppA). These dinucleotides have been proposed to act as modulators of the heat-shock response and stress response. ATP + L-lysine + tRNA(Lys) = AMP + diphosphate + L-lysyl-tRNA(Lys) Binds 3 Mg(2+) ions per subunit. The third one is coordinated by ATP. Homodimer. There are two lysyl-tRNA ligases in E.coli: lysS is expressed constitutively, while lysU is heat inducible. Belongs to the class-II aminoacyl-tRNA synthetase family.