MOLECULAR CHARACTERIZATION OF THE LINCOMYCIN-PRODUCTION GENE-CLUSTER OF STREPTOMYCES LINCOLNENSIS-78-11

The lincomycin (LM)-production gene cluster of the overproducing strai n Streptomyces lincolnensis 78-11 was cloned, analysed by hybridizatio n, as well as by DNA sequencing, and compared with the respective geno me segments of other lincomycin producers. The lmb/lmr gene cluster is composed of 27 open reading frames with putative biosynthetic or regu latory functions (Imb genes) and three resistance (lmr) genes, two of which, lmrA and lmrC, flank the cluster. A very similar overall organi zation of the lmb/lmr cluster seems to be conserved in four other LM p roducers, although the clusters are embedded in non-homologous genomic surroundings. In the wild-type strain (S. lincolnensis NRRL2936), the lmb/lmr-cluster apparently is present only in single copy. However, i n the industrial strain S. lincolnensis 78-11 the nonadjacent gene clu sters for the production of LM and melanin (melC) both are duplicated on a large (0.45-0.5 Mb) fragment, accompanied by deletion events. Thi s indicates that enhanced gene dosage is one of the factors for the ov erproduction of LM and demonstrates that large-scale genome rearrangem ents can be a result of classical strain improvement by mutagenesis. O nly a minority of the putative Lmb proteins belong to known protein fa milies. These include members of the gamma-glutamyl transferases (LmbA ), amino acid acylases (LmbC), aromatic amino acid aminotransferases ( LmbF), imidazoleglycerolphosphate dehydratases (LmbK), dTDP-glucose sy nthases (LmbO), dTDP-glucose 4,6-dehydratases (LmbM) and (NDP-) ketohe xose (or ketocyclitol) aminotransferases (LmbS). In contrast to earlie r proposals on the biosynthetic pathway of the C-8 sugar moiety (methy lthiolincosaminide), this branch of the LM pathway actually seems to b e based on nucleotide-activated sugars as precursors.