2 MULTIFUNCTIONAL PEPTIDE SYNTHETASES AND AN O-METHYLTRANSFERASE ARE INVOLVED IN THE BIOSYNTHESIS OF THE DNA-BINDING ANTIBIOTIC AND ANTITUMOR AGENT SAFRAMYCIN MX1 FROM MYXOCOCCUS-XANTHUS

Saframycin Mx1 is a DNA-binding antibiotic and antitumour agent produc ed by Myxococcus xanthus. It is a heterocyclic quinone, thought to be synthesized via the linear pepide intermediate AlaGlyTyrTyr. Analysis of 14.1 kb DNA sequence involved in saframycin production revealed gen es for two large multifunctional peptide synthetases of 1770 and 2605 amino acids, respectively, and a putative O-methyltransferase of 220 a mino acids. The three ORFs read in the same direction and are separate d by short non-translated gaps of 44 and 49 bp. The peptide synthetase s contain two amino-acid-activating domains each. The first domain lac ks two of the most conserved 'core' sequences, and the last domain is followed by a putative reductase functionality, not previously seen in peptide synthetases. Complementation tests showed that antibiotic-non producing mutant strains lacking one of the peptide synthetases secret e a substrate, presumably a modified amino acid precursor, that can be used by O-methyltransferase-deficient mutant strains to synthesise sa framycin Mx1.