The blasticidin S biosynthesis gene cluster from Streptomyces griseochromogenes: Sequence analysis, organization, and initial characterization

Blasticidin S is a potent antifungal and cytotoxic petidyl nucleoside antibiotic from Streptomyces griseochromogenes. The mixed biosynthesis of the compound is evident from the three distinct structural components: a cytosine base, an amino deoxyglucuronic acid, and N-methyl β arginine. The blasticidin S biosynthesis gene cluster was cloned from S. griseochromogenes and the pathway heterologously expressed in S. lividans from a cosmid harboring a 36.7-kb fragment of S. griseochromogenes DNA. The complete DNA sequence of this insert has now been determined and evidence suggests a Contiguous 20-kb section defines the blasticidin S biosynthesis cluster. The predicted funtions of several open reading frames are consistent with the expected biochemistry and include an arginine 2,3-aminomutase, a cytosylglucoronic acid synthase, and a guanidino N-methyltransferase. Insight into other steps in the assembly of blasticidin S was evident from sequence homology with proteins of known function and heterologous expression of fragments of the cluster. Additionally, the gene that directs the production of free cytosine, blsM, was subcloned and expressed in Escherichia coli. Characterization of BlsM revealed that cyticidine monophosphate serves as the precursor to cytosine.