Acetohydroxy acid synthase III activity in an ilvI mutant of E. coli K-12

ilvI and ilvH are the structural genes for the two subunits I and H of acetohydroxy acid synthase III, a key enzyme in isoleucine, leucine and valine biosynthesis in Escherichia coli K-12. Deletion of 100 base pairs at the promoter distal end of ilvH abolished the production of the H polypeptide in vivo, reduced dramatically the enzyme level, enhanced 2-fold the Km for pyruvate and rendered the enzyme resistant to valine inhibition, without affecting the rate of gene expression.