Identification and nucleotide sequence of the class E tet regulatory elements and operator and inducer binding of the encoded purified Tet repressor

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Abstract
The regulatory region and repressor (tetR E) gene from the class E tetracycline resistance determinant previously isolated from Enterobacteriaceae have been identified and completely sequenced. The regulatory region is located between the resistance gene and the tetR gene which have opposite polarity. The tetR gene encodes a protein consisting of 211 amino acids with a calculated molecular weight of 23.6 kDa. Cloning of the tetR gene under transcriptional control of the λ P L promoter leads to overexpression of a polypeptide with an apparent molecular weight of 26 kDa. The purified protein binds sequence specifically to DNA fragments containing putative tet operators. This property is lost in the presence of tetracycline. The relationship of the tetR E sequence to four known tetracycline resistance determinants is discussed.