CHARACTERIZATION OF AN OXYTETRACYCLINE-RESISTANCE GENE, OTRA, OF STREPTOMYCES-RIMOSUS

The sequence of a 2657 bp DNA fragment containing the coding and regulatory regions of the oxytetracycline (OTC)-resistance gene, otrA, from the OTC producer Streptomyces rimosus was determined. The predicted amino acid sequence of OtrA had extensive identity with tetracycline-resistance genes from other bacteria which mediate resistance via non-covalent ribosomal modification. The N-terminal domain had extremely high identity with the GTP-binding sites of elongation factors, such as EF-G and EF-Tu, suggesting that binding and hydrolysis of GTP is important to the function of the protein. Significant identity with EF-G was present throughout the polypeptide. Transcriptional activity upstream of the otrA coding region was investigated. An Escherichia coli-type promoter, otrAp1, was identified. Transcriptional readthrough of otrA from the upstream gene (otcZ) was also detected in S. rimosus cultures. A divergent promoter activity was identified with subclones of the OtrA fragment in promoter probe vectors analysed in Streptomyces lividans. However, this activity was not identified in a subclone containing more than half of the otrA coding sequence in S. lividans or at all in S. rimosus, indicating that OtrA negatively regulates the expression of the divergent transcript. The data are consistent with regulation of antibiotic production by OtrA to prevent 'suicide'.