title: Constitutive expression of tetracycline resistance mediated by a Tn10-like element in Haemophilus parainfluenzae results from a mutation in the repressor gene.
abstract: The Tn10-like constitutively expressed tetracycline resistance determinant from a Haemophilus parainfluenzae strain was cloned in Escherichia coli. Toxicity resulting from expression on multicopy plasmids necessitated its being cloned on a low-copy plasmid vector or in cells containing the Tn10-encoded repressor. Constitutive expression of tetracycline resistance was found to result from the synthesis of a truncated inactive repressor molecule. Instead of the 23-kilodalton repressor found in other Tn10-containing strains, this determinant encoded a 14.5-kilodalton molecule. The DNA sequence of the 700-base-pair region spanning the repressor gene and promoter-operator regions of the Haemophilus determinant was identical to that of the same region of Tn10, except for the absence of a single T X A base pair in the repressor gene. This deletion leads to premature termination of the protein. Antisera to the repressor suggested that the repressor was also absent in a second independently isolated H. parainfluenzae strain bearing a Tn10-like constitutive tetracycline resistance determinant.
mesh_terms: D003001:Cloning, Molecular; D004251:DNA Transposable Elements; D004352:Drug Resistance, Microbial; D005796:Genes; D005798:Genes, Bacterial / Q000187:drug effects*; D006190:Haemophilus / Q000187:drug effects / Q000235:genetics*; D009154:Mutation; D010957:Plasmids; D012097:Repressor Proteins / Q000235:genetics*; D013752:Tetracycline / Q000494:pharmacology*; D014157:Transcription Factors / Q000235:genetics*
chemical_list: D004251:DNA Transposable Elements; D012097:Repressor Proteins; D014157:Transcription Factors; D013752:Tetracycline