Catalyzes the specific attachment of an amino acid to its cognate tRNA in a 2 step reaction: the amino acid (AA) is first activated by ATP to form AA-AMP and then transferred to the acceptor end of the tRNA. ATP + L-lysine + tRNA(Lys) = AMP + diphosphate + L-lysyl-tRNA(Lys) Homodimer. RNAi-mediated knockdown results in an arrest at an early larval stage. In adults, causes a 80 percent reduction in progeny size and a 50 percent increase in eIF2alpha phosphorylation. It is likely that the same gene provides both this cytoplasmic isoform and an additional mitochondrial isoform. Belongs to the class-II aminoacyl-tRNA synthetase family.