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

DNA Inversion in the Tail Fiber Gene Alters the Host Range Specificity of Carotovoricin Er, a Phage-Tail-Like Bacteriocin of Phytopathogenic Erwinia carotovora subsp. carotovora Er

Carotovoricin Er is a phage-tail-like bacteriocin produced by Erwinia carotovora subsp. carotovora strain Er, a causative agent for soft rot disease in plants. Here we studied binding and killing spectra of carotovoricin Er preparations for various strains of the bacterium (strains 645Ar, EC-2, N786, and P7) and found that the preparations contain two types of carotovoricin Er with different host specificities; carotovoricin Era possessing a tail fiber protein of 68 kDa killed strains 645Ar and EC-2, while carotovoricin Erb with a tail fiber protein of 76 kDa killed strains N786 and P7. The tail fiber proteins of 68 and 76 kDa had identical N-terminal amino acid sequences for at least 11 residues. A search of the carotovoricin Er region in the chromosome of strain Er indicated the occurrence of a DNA inversion system for the tail fiber protein consisting of (i) two 26-bp inverted repeats inside and downstream of the tail fiber gene that flank a 790-bp fragment and (ii) a putative DNA invertase gene with a 90-bp recombinational enhancer sequence. In fact, when a 1,400-bp region containing the 790-bp fragment was amplified by a PCR using the chromosomal DNA of strain Er as the template, both the forward and the reverse nucleotide sequences of the 790-bp fragment were detected. DNA inversion of the 790-bp fragment also occurred in Escherichia coli DH5α when two compatible plasmids carrying either the 790-bp fragment or the invertase gene were cotransformed into the bacterium. Furthermore, hybrid carotovoricin CGE possessing the tail fiber protein of 68 or 76 kDa exhibited a host range specificity corresponding to that of carotovoricin Era or Erb, respectively. Thus, a DNA inversion altered the C-terminal part of the tail fiber protein of carotovoricin Er, altering the host range specificity of the bacteriocin