tet promoter

The tet promoter is found at the beginning of the tetracycline resistance region in plasmids containing class C resistance determinants, like pACYC184, pBR322 or pSC101. It contains palindromic operator sequences (O1 and O2). The tet promoter is constitutive active in absence of the tetracycline repressor TetR. In the presence of the tetracycline repressor TetR and in the absence of tetracycline TetR binds to the operator sequence and thereby avoids expression from the tet promoter. When tetracycline diffuses into the cell an allosteric conformational change in the repressor protein occures and the repressor is released from the DNA and expression from the tet promoter is induced.