Characterization of the tet(M) determinant of Tn916: evidence for regulation by transcription attenuation.
The nucleotide sequence of the tetracycline resistance determinant tet(M), located on conjugative transposon Tn916 of Enterococcus faecalis, was determined and found to encode a 72,486-dalton protein exhibiting a high degree of homology with other tet(M) determinants. A short open reading frame corresponding to a 28-amino-acid peptide and containing a number of inverted repeat sequences was noted immediately upstream of tet(M), suggesting that regulation might occur by a mechanism involving transcriptional attenuation. Transcription analyses found this to indeed be the case, showing that the expression of tet(M) resulted from an extension of a small transcript representing the upstream leader region into the resistance determinant. Exposure of cells to tetracycline resulted in a significant increase in the amount of tet(M) transcription; this increase could be explained on the basis of increased transcriptional read-through from the upstream transcript. A model suggesting how transcriptional attenuation might operate in this system is presented.
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Department of Biologic Science, School of Dentistry, University of Michigan, Ann Arbor 48109.
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Clewell
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D000595:Amino Acid Sequence; D001483:Base Sequence; D004251:DNA Transposable Elements; D004269:DNA, Bacterial / Q000032:analysis; D013293:Enterococcus faecalis / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics; D008969:Molecular Sequence Data; D013753:Tetracycline Resistance / Q000235:genetics*; D014158:Transcription, Genetic
D004251:DNA Transposable Elements; D004269:DNA, Bacterial