TetR family regulators are involved in the transcriptional control of multidrug efflux pumps, pathways for the biosynthesis of antibiotics, response to osmotic stress and toxic chemicals, control of catabolic pathways, differentiation processes, and pathogenicity [1]. The TetR proteins identified in overm ultiple genera of bacteria and archaea share a common helix-turn-helix (HTH) structure in their DNA-binding domain. However, TetR proteins can work in different ways: they can bind a target operator directly to exert their effect (e.g. TetR binds Tet(A) gene to repress it in the absence of tetracycline), or they can be involved in complex regulatory cascades in which the TetR protein can either be modulated by another regulator or TetR can trigger the cellular response [1]. TetR regulates the expression of the membrane-associated tetracycline resistance protein, TetA, which exports the tetracycline antibiotic out of the cell before it can attach to the ribosomes and inhibit protein synthesis [2]. TetR blocks transcription from the genes encoding both TetA and TetR in the absence of antibiotic. The C-terminal domain is multi-helical and is interlocked in the homodimer with the helix-turn-helix (HTH) DNA-binding domain [2]. This entry represents the C-terminal domain present in family members such as HTH-type transcriptional repressor KstR2 as well as fatty acid metabolism regulator proteins. In Mycobacterium smegmatis, KstR2 is involved in involved in cholesterol catabolism [3], while YsiA in Bacillus subtilis is involved in fatty acid degradation [4].

1: The TetR family of transcriptional repressors. Ramos JL, Martinez-Bueno M, Molina-Henares AJ, Teran W, Watanabe K, Zhang X, Gallegos MT, Brennan R, Tobes R; Microbiol Mol Biol Rev. 2005;69:326-356. PMID:15944459

2: The complex formed between Tet repressor and tetracycline-Mg2+ reveals mechanism of antibiotic resistance. Kisker C, Hinrichs W, Tovar K, Hillen W, Saenger W; J Mol Biol. 1995;247:260-280. PMID:7707374

3: Cholesterol utilization in mycobacteria is controlled by two TetR-type transcriptional regulators: kstR and kstR2. Kendall SL, Burgess P, Balhana R, Withers M, Ten Bokum A, Lott JS, Gao C, Uhia-Castro I, Stoker NG; Microbiology. 2010;156:1362-1371. PMID:20167624

4: Organization and function of the YsiA regulon of Bacillus subtilis involved in fatty acid degradation. Matsuoka H, Hirooka K, Fujita Y; J Biol Chem. 2007;282:5180-5194. PMID:17189250