Translational attenuation control of ermSF, an inducible resistance determinant encoding rRNA N-methyltransferase from Streptomyces fradiae.

An inducible resistance determinant, ermSF, from the tylosin producer Streptomyces fradiae NRRL 2338 has been cloned, sequenced, and shown to confer inducible macrolide-lincosamide-streptogramin B resistance when transferred to Streptomyces griseofuscus NRRL 23916. From mapping studies with S1 nuclease to locate the site of transcription initiation, the ermSF message contains a 385-nucleotide 5' leader sequence upstream from the 960-nucleotide major open reading frame that encodes the resistance determinant. On the basis of the potential secondary structure that the ermSF leader can assume, a translational attenuation model similar to that for ermC is proposed. The model is supported by mutational analysis involving deletions in the proposed attenuator. By analysis with restriction endonucleases, ermSF is indistinguishable from the tlrA gene described by Birmingham et al. (V. A. Birmingham, K. L. Cox, J. L. Larson, S. E. Fishman, C. L. Hershberger, and E. T. Seno, Mol. Gen. Genet. 204:532-539, 1986) which comprises one of at least three genes from S. fradiae that can confer tylosin resistance when subcloned into S. griseofuscus. When tested for inducibility, ermSF appears to be strongly induced by erythromycin, but not by tylosin

Transcriptional attenuation control of the tylosin-resistance gene tlrA in Streptomyces fradiae

The tylosin producer Streptomyces fradiae contains four known resistance genes, two of which (tlrA and tlrD) encode methyltransferases that act on ribosomal RNA at a common site. Expression of tlrA is regulated via transcriptional attenuation. A short transcript, only 411 nucleotides long, terminates 27 nucleotides into the methylase‐coding sequence in the uninduced state. Induction of tlrA is proposed to involve a ribosome‐mediated conformational change within the mRNA leader that allows transcription to continue beyond the attenuation site, resulting in a transcript about 1450 nucleotides long. Transplantation of tlrD and/or tlrA into Streptomyces albus revealed that the induction specificity of tlrA depends upon the state of the ribosomes and is significantly altered in strains also expressing tlrD