FIGURE 2.

Variety of one-component TFs found in nature. (A) ArgR (3LAJ, Cherney et al., 2010) represses the transcription of the biosynthetic genes of the arginine operon. ArgR is a wHTH transcriptional aporepressor activated by the corepressor arginine, so that the regulated operon is not transcribed when the effector is present. (B) LacI (1EFA, Bell et al., 1998) inhibits expression of the lac operon. When the sugar allolactose is present, its binding to the C-terminal domain of dimeric LacI produces a conformational change that inhibits DNA binding by the N-terminal HTH. (C) NikR (2HZV, (Schreiter et al., 2006) is a ligand dependent aporepressor that only binds the operon when Ni⁺² is bound. (D) TetR (1QPI, Orth et al., 2000) is a HTH repressor that senses the presence of the antibiotic tetracycline. (E) FadR (1HW2, Xu et al., 2001) contains an N-terminal wHTH motif connected to a C-terminal EBD similar to TetR family EDBs. However, FadR effectors are acyl-CoAs instead of antibiotics. (F) cAMP receptor protein or CRP (1CGP, Schultz et al., 1991) is a transcriptional activator. cAMP allows the binding of the CRP C-terminal HTH motif to the operator of several catabolic operons. There, CRP-cAMP interacts with RNApol, allowing the transcription of the corresponding operons. In this figure, as well as in the following figures, DBDs are colored in green and EBDs in magenta. The number of amino acids of each TF is also shown.