Nucleotide sequence of the aknA region of the aklavinone biosynthetic gene cluster of Streptomyces galilaeus.

A 3.4-kb BamHI fragment that is assumed to be a part of the aklavinone biosynthetic gene cluster of Streptomyces galilaeus 3AR-33 and contains the genes required for the early stage of polyketide biosynthesis was sequenced. The nucleotide sequence of the region that hybridizes to the actIII probe reveals the presence of a gene, aknA, whose deduced protein product is very similar to the ActIII protein and other known oxidoreductases. The predicted AknA protein is believed to be responsible for catalyzing the reduction of the keto group at the ninth carbon from the carboxyl terminus of the assembled polyketide to the corresponding secondary alcohol. The predicted AknA protein has a calculated molecular mass of 27,197 Da (261 amino acids) and the highly conserved sequence Gly-Xaa-Gly-Xaa-Xaa-Ala commonly seen in oxidoreductases. Cloning and sequence analysis of the aknA region of the 2-hydroxyaklavinone-producing strain S. galilaeus ANR-58 identified an alteration in the gene, confirming that the aknA gene is essential for aklavinone biosynthesis.