ANALYSIS OF ERYBI ERYBIII AND ERYBVII FROM THE ERYTHROMYCIN BIOSYNTHETIC GENE-CLUSTER IN SACCHAROPOLYSPORA-ERYTHRAEA

The gene cluster (ery) governing the biosynthesis of the macrolide ant ibiotic erythromycin A by Saccharopolyspora erythraea contains, in add ition to the eryA genes encoding the polyketide synthase, two regions containing genes for later steps in the pathway. The region 5' of eryA that lies between the known genes ermE (encoding the erythromycin res istance methyltransferase) and eryBIII (encoding a putative S-adenosyl methionine-dependent methyltransferase), and that contains the gene er yBI (orf2), has now been sequenced. The inferred product of the eryBI gene shows striking sequence similarity to authentic beta-glucosidases . Specific mutants were created in eryBI, and the resulting strains we re found to synthesise erythromycin A, showing that this gene, despite its position in the biosynthetic gene cluster, is not essential for e rythromycin biosynthesis. A mutant in eryBIII and a double mutant in e ryBI and eryBIII were obtained and the analysis of novel erythromycins produced by these strains confirmed the proposed function of EryBIII as a C-methyltransferase. Also, a chromosomal mutant was constructed f or the previously sequenced ORF19 and shown to accumulate erythronolid e B, as expected for an eryB mutant and consistent with its proposed r ole as an epimerase in dTDP-mycarose biosynthesis.