Abstract: A bacterium belonging to the genus Escherichia, which is transformed by introducing, into its cells, a DNA coding for a dihydrodipicolinate synthase originating from a bacterium belonging to the genus Escherichia having mutation to desensitize feedback inhibition by L-lysine and a DNA coding for an aspartokinase III originating from a bacterium belonging to the genus Escherichia having mutation to desensitize feedback inhibition by L-lysine; preferably a bacterium belonging to the genus Escherichia in which a dihydrodipicolinate reductase gene and a diaminopimelate dehydrogenase gene originating from Brevibacterium lactofermentum (or a succinyldiaminopimelate transaminase gene and a succinyldiaminopimelate deacylase gene) are further enhanced, is cultivated in an appropriate medium, L-lysine is produced and accumulated in a culture thereof, and L-lysine is collected from the culture.

Abstract: A bacterium belonging to the genus Serratia, which is transformed by introducing into its cells, a DNA coding for a dihydrodipicolinate synthase originating from a bacterium belonging to the genus Escherichia or Serratia having mutation to desensitize feedback inhibition by L-lysine and a DNA coding for an aspartokinase originating from a bacterium belonging to the genus Escherichia or Serratia having mutation to desensitize feedback inhibition by L-lysine is cultivated in an appropriate medium, L-lysine is produced and accumulated in a culture thereof, and L-lysine is collected from the culture.

Abstract: Recombinant DNA replicable in microorganisms belonging to the genus Corynebacterium, which contains a DNA fragment coding for an aspartokinase .alpha.-subunit protein originating from a bacterium belonging to the genus Corynebacterium, in which synergistic feedback inhibition by L-lysine and L-threonine is substantially desensitized, and a DNA fragment coding for an aspartokinase .beta.-subunit protein originating from a bacterium belonging to the genus Corynebacterium, in which synergistic feedback inhibition by L-lysine and L-threonine is substantially desensitized, is introduced into a microorganism belonging to the genus Corynebacterium. Thus a transformant having enhanced production and excretion speeds of L-lysine is obtained. The transformant is cultivated in an appropriate medium, and produced L-lysine is separated.

Abstract: A DNA containing a gene which codes for aspartokinase III originating in Escherichia bacteria and which has in the coding region a mutation which releases the feedback inhibition by lysine on the aspartokinase III, a recombinant DNA wherein the DNA is linked to a vector DNA capable of autonomous replication in Escherichia bacteria, a microorganism belonging to the genus Escherichia which has been transformed by the introduction of the above mentioned recombinant DNA into the cells thereof, and a method for the production of L-threonine which comprises culturing the microorganism in a fermentation medium, producing and accumulating L-threonine in the culture medium, and collecting the L-threonine from said-culture medium. Escherichia bacteria-derived AK III genes are obtained which sufficiently release the feedback inhibition due to lysine.