Dna which encodes aspartokinase iii - mutants and their use for the production of l - threonine by fermentation

摘要

A DNA containing a gene that codes for aspartokinase III from a bacterium of the genus Escherichia and has in the coding region thereof a variation that releases the inhibition of aspartokinase III feedback by lysine; a recombinant DNA comprising the above DNA joined to a vector DNA capable of autonomous replication in the cell of a bacterium of the genus Escherichia; a micro-organism of the genus Escherichia, that has been transformed by introducing the recombinant DNA into the cells; and a process for producing L-threonine by culturing the micro-organism in a fermentation medium to accumulate L-threonine in the medium and harvesting the same from the medium. The invention process has provided AK III genes originating in a bacterium of the genus Escherichia and sufficiently released from the feedback inhibition caused by lysine. An improved threonine-producing bacterium has been obtained by introducing the above genes into a conventional threonine-producing bacterium. The invention successfully provides a process for producing L-threonine by an improved fermentation method using the above threonine-producing bacterium.