Stimulates activity of the acetolactate synthase catalytic subunit ilv1. Amino-acid biosynthesis; L-isoleucine biosynthesis; L-isoleucine from 2-oxobutanoate: step 1/4. Amino-acid biosynthesis; L-valine biosynthesis; L-valine from pyruvate: step 1/4. Belongs to the acetolactate synthase small subunit family.