The Tn10 tetR gene encodes the repressor that regulates transcription of the Tnl0 tetracycline resistance determinant. We have determined the DNA sequence of the tetR gene and a 905 base pair region immediately 3′ to tetR. The tetR gene is located on a 701 base pair HincII restriction fragment. Deletions at either end of this region eliminate synthesis of the wild-type tetR protein in E. coli minicells, and eliminate tetR activity as measured by repression of β-galactosidase synthesis in tetA-lacZ operon fusion strains. Taken together, the DNA sequence and the genetic data indicate that tetR encodes a 207 amino acid protein with a calculated molecular weight of 23,328. This value is in good agreement with estimates of 23,000-25,000 based on electrophoretic mobility in SDS-polyaerylamide gels. There is 47% amino acid sequence homology between the deduced sequences of the Tn10 and RPl/Tnl721 tetR proteins. There is, in addition, significant amino acid sequence homology between an NH2-terminal region of the Tnl0 tetR repressor and the DNA recognition regions of other DNA-binding proteins.
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