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Tetracycline (tc) is a broad family of antibiotics to which bacteria have evolved resistance. Tc normally kills bacteria by binding to the bacterial ribosome and halting protein synthesis. The expression of tc resistance genes is regulated by Tet Repressor Protein, called TetR. More specifically, TetR represses the expression of TetA, a membrane protein that pumps out substances toxic to the bacteria, by binding the TetA operator. In tc resistant bacteria, TetA will pump out tc before it can bind to the ribosome. Therefore, TetR may have an important role in helping scientists to better understand mechanisms of antibiotic resistance and how to treat antibiotic resistant bacteria. TetR is one of many proteins in the TetR protein family, which is so named because TetR is the most well characterized member.

TetR is used in artificially engineered gene regulatory networks because of its capacity for fine regulation. In the absence of tc, basal expression of TetR is very low, but expression rises sharply in the presence of even a minute quantity of tc through a positive feedback mechanism. TetR is present in the widely used E. coli cloning vector pBR322