A SELF-DEFENSE GENE HOMOLOGOUS TO TETRACYCLINE EFFLUXING GENE ESSENTIAL FOR ANTIBIOTIC PRODUCTION IN STREPTOMYCES-AUREOFACIENS

By Northern blot analyses with DNA probes carrying 6-demethylchlortetr acycline (6-DCT) biosynthetic genes from Streptomyces aureofaciens NRR L3203, a highly expressed gene (tcrC) was detected in a high titer pro ducing mutant derived from the parental strain NRRL3203 by NTG mutagen esis, The analysis of the nucleotide sequence of the 2.8-kb BamHI frag ment containing tcrC gene showed that the predicted tcrC gene product is a protein consisting of 512 amino acids. The deduced amino acid seq uence had a high level identity with that of the self-defense gene (te t347) of Streptomyces rimosus, known to mediate oxytetracycline efflux . The tcrC gene-inactivated strains generated from strain NRRL3203 by gene replacement had a 90% decrease in the level of resistance to tetr acycline and the antibiotic productivity when compared with the parent al strain.