Biosynthesis pathways of branched-chain amino acids (valine, leucine, isoleucine) are controlled by a complex regulatory system. To improve valine production by C. glutamicum, modifications (mutations) of promotersof genes ilvA, ilvB, ilvD, ilvE and leuA were constructed within the chromosome. The modulations of promoter strength (up or down mutations) resulted in an efficient valine produce