SMALL SUBUNIT OF ISOZYME III AND ISOZYME III OF ACETOHYDROXYACID SYNTHETASE FROM ESCHERICHIA COLI, DNA FRAGMENT (VARIANTS), STRAIN OF BACTERIUM ESCHERICHIA COLI AS PRODUCER OF L-VALINE (VARIANTS) AND METHOD FOR PREPARING L-VALINE Russian patent published in 2003 - IPC

FIELD: molecular biology, biochemistry, amino acids, microbiology. SUBSTANCE: invention relates to method for preparing L-valine. The strain of E. coli comprising DNA encoding isozyme III of acetohydroxyacid synthetase from Escherichia coli is cultured in nutrient medium providing production and accumulation of L-valine in nutrient medium and isolation of L-valine from nutrient medium. Activity of isozyme III of synthetase is not inhibited by L-valine and exhibits catalytic activity in two reactions: reaction of synthesis of α-acetolactate from pyruvate and reaction of synthesis of α-aceto-α-hydroxybutyrate from α-ketobutyrate and pyruvate. Isozyme III in small subunit comprises mutation in position 17 with substitution of serine for phenylalanine or in position 29 with substitution of asparagine residue for lysine or tyrosine, or mutation resulting to deletion of C-terminal site beginning from amino acid in position 91 or to substitution of glycine residue in position 14 for aspartic acid residue. Amino acid sequences are given in the description. Strains of E. coli comprise corresponding DNA fragments. EFFECT: enhanced expression of L- valine. 10 cl, 2 dwg, 4 tbl