the l - lysine - producing ability and the l - lysine - producing speed are improved in a coryneform bacterium harboring an aspartokinase in which feedback inhibition by l - lysine and l - threonine is substantially desensitized , by successively enhancing dna coding for a dihydrodipicolinate reductase , dna coding for a dihydrodipicolinate synthase , dna coding for a diaminopimelate decarboxylase , and dna coding for a diaminopimelate dehydrogenase .