Cloning, sequencing and function of sanB, a gene related to nikkomycin biosynthesis of Streptomyces ansochromogenes

A 6.0 kb DNA fragment related to nikkomycin biosynthesis was cloned from ni kkomycin-producing Streptomyces ansochromogenes 7100. Sequence analysis sho wed that the 1.9 kb Tth111 I fragment, a part of the 6.0 kb DNA fragment, c ontains one complete ORF designated sanB (GenBank accession No. AF224501), which is composed of 1740 bp encoding a protein consisting of 580 amino aci d residues. Its start codon is GTG at 100 bp position and stop codon is IGA at 1840-bp position. Database searching indicated that the deduced protein of sanB is homologous to the histidinol-phosphate aminotransferase in Stre ptomyces coelicolor with 31% identities and 47% positives. Gene disruption was performed to study the function of sanB. It was found that disruptants of sanB lost the ability to synthesize nikkomycin, which reveals that sanB is a novel gene essential for nikkomycin biosynthesis.