Regulatory subunit of mitochondrial acetolactate synthase, which catalyzes the first of a series of common steps in the biosynthesis of the branched-chain amino acids. Stimulates activity of the acetolactate synthase catalytic subunit ILV2 seven- to tenfold and confers sensitivity to inhibition by valine and activation by ATP. 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. The acetolactate synthase complex contains the catalytic regulatory subunit ILV2 and the regulatory small subunit ILV6. Present with 15800 molecules/cell in log phase SD medium. Belongs to the acetolactate synthase small subunit family.