TRANSCRIPTIONAL ATTENUATION CONTROL OF THE TYLOSIN-RESISTANCE GENE TLRA IN STREPTOMYCES-FRADIAE

The tylosin producer Streptomyces fradiae contains four known resistan ce 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 nucleot ides long, terminates 27 nucleotides into the methylase-coding sequenc e in the uninduced state. Induction of tlrA ii; proposed to involve a ribosome-mediated conformational change within the mRNA leader that al lows transcription to continue beyond the attenuation sites, resulting in a transcript about 1450 nucleotides long. Transplantation of tlrD and/or tlrA into Streptomyces albus revealed that the induction specif icity of tlrA depends upon the state of the ribosomes and is significa ntly altered in strains also expressing tlrD.