Process for constructing amino acid-producing bacterium and process for producing amino acid by fermentation method with the use of the thus constructed amino acid-producing bacterium

A method of producing coryneform bacteria having an improved amino acid-or nucleic acid-productivity comprises the steps of introducing a mutation in a promoter sequence of amino acid- or nucleic acid-biosynthesizing genes on a chromosome of a coryneform bacterium to make it dose to a consensus sequence or introducing a change in a promoter sequence of amino acid- or nucleic acid-biosynthesizing genes on a chromosome of a coryneform bacterium by gene recombination to make it close to a consensus sequence, to obtain mutants of the coryneform amino acid- or nucleic acid-producing microorganism, culturing the mutants and select a mutant capable of producing the intended amino acid or nucleic acid in a large amount. This method can construct a mutant capable of suitably enriching or controling the expression of an intended gene without using a plasmid and also capable of producing amino acids in a high yield, by the recombination or mutation.