Alternative method for site-directed mutagenesis of complex polyketide synthase in Streptomyces albus JA3453
This study was supported by the grants from the “973 Program” of the Ministry of Science and Technology (No. 2003CB114205), the National Natural Science Foundation of China (No. 30470941), and the Shanghai Municipal Council of Science and Technology (No. 04JC14058)
Abstract
Sequence analysis of oxazolomycin (OZM) biosynthetic gene cluster from Streptomyces albus JA3453 revealed a gene, ozmH, encoding a hybrid polyketide and non-ribosomal pep-tide enzyme. Tandem ketosynthase (KS) domains (KS10–1 and KS10–2) were characterized and they show significant homol-ogy with known KSs. Using an alternative method that involves RecA-mediated homologous recombination, the negative selection marker sacB gene, and temperature-sensitive replications, site-directed mutagenesis of the catalytic triad amino acid cysteines were carried out in each of the tandem KS domains totest the function they play in OZM biosynthesis. HPLC-mass spectrometry analysis of the resulting mutant strains showed that KS10–2 is essential for OZM biosynthesis but KS10–1 is not indispensable and might serve as a “redundant” domain. These results confirmed the existence of an “extra domain” in complex polyketide synthase.