A 2.8-kb BamHl fragment was cloned from the cosmid library of Streptomyces ansochromogenes by using the 1.35-kb BamHI-ApaI fragment of sanO involved in nikkomycin biosynthesis as a probe. Sequence analysis showed that the BamHl fragment contains an open reading frame with 1191 bp, which was designated sanQ. In search of databases, the deduced product of sanQ gene has 56% similarity to the cytochrome P450. sanQ gene was inactivated by insertion of a kanamycin resistance gene. The resulting disruptants failed to produce nikkomycin X, but nikkomycin Z was at the same level as the wild type, indicating that sanQ is essential for the biosynthesis of nikkomycin X.