PRISTINAMYCIN-I BIOSYNTHESIS IN STREPTOMYCES-PRISTINAESPIRALIS - MOLECULAR CHARACTERIZATION OF THE FIRST 2 STRUCTURAL PEPTIDE SYNTHETASE GENES

Two genes involved in the biosynthesis of the depsipeptide antibiotics pristinamycins I (PI) produced by Streptomyces pristinaespiralis were cloned and sequenced. The 1.7-kb snbA gene encodes a 3-hydroxypicolin ic acid:AMP ligase, and the 7.7-kb snbC gene encodes PI synthetase 2, responsible for incorporating L-threonine and L-aminobutyric acid in t he PI macrocycle. snbA and snbC, which encode the two first structural enzymes of PI synthesis, are not contiguous. Both genes are located i n PI-specific transcriptional units, as disruption of one gene or the other led to PI-deficient strains producing normal levels of the polyu nsaturated macrolactone antibiotic pristinamycin II, also produced by S. pristinaespiralis. Analysis of the deduced amino acid sequences sho wed that the SnbA protein is a member of the adenylate-forming enzyme superfamily and that the SnbC protein contains two amino acid-incorpor ating modules and a C-terminal epimerization domain. A model for the i nitiation of PI synthesis analogous to the established model of initia tion of fatty acid synthesis is proposed.