NOVELTY - A substantially purified polypeptide capable of initiating the conversion of 2-keto-3-methylvalerate to a C6-C9 keto acid, or the conversion of a C6-C9 keto acid to a C5-C8 alcohol, is new.    USE - The polypeptide, polynucleotide and microorganism are useful for producing biofuels and higher alcohols including C5- C8 alcohols.    ADVANTAGE - The present invention provides metabolically-modified microorganisms useful for producing biofuels.    DETAILED DESCRIPTION - A substantially purified polypeptide comprises at least 80% identical to SEQ ID NO: 2, having a mutation in any of the following residues Asp430, Ala453, Ala460 or Gly462 to remove leucine feedback inhibition and may include at least one additional mutation selected from Ser139Gly, Asn167Ala, Asn167Leu, and His97Ala, where the polypeptide is capable of initiating the conversion of 2-keto-3-methylvalerate to a C6-C9 keto acid; or a substantially purified polypeptide comprises at least 80% identical to SEQ ID NO: 18, having a Val461Ala mutation and may include at least one additional mutation selected from Met538Ala, Met538Leu, Phe381Ala and Phe381Leu, where the polypeptide is capable of initiating the conversion of a C6-C9 keto acid to a C5-C8 alcohol. INDEPENDENT CLAIMS are: (1) an isolated polynucleotide encoding a polypeptide above, or an isolated polynucleotide comprising a sequence that encodes a polypeptide of SEQ ID NO: 2 having a Gly462Asp mutation or a polypeptide of SEQ ID NO: 18 having a Val461Ala mutation; (2) a recombinant microorganism that expresses the polypeptide above or comprising the polynucleotide of (1); (3) a recombinant microorganism that produces a C5, C6, C7 or C8 alcohol comprising a recombinant metabolic pathway and a mutant 2-isopropylmalate synthase that converts a 2-keto-3-methylvalerate to a C6-C9 keto acid; and (4) an isolated polynucleotide encoding a mutant 2- isopropylmalate synthase derived from Escherichia coli comprising a Gly462Asp/Ser139Gly/Asn167Ala triple mutant or a Gly462Asp/Ser139Gly/His97Ala/Asn167Ala quadruple mutant.