TetR

Tc normally kills bacteria by binding to the bacterial ribosome and halting protein synthesis.

[2] TetR is used in artificially engineered gene regulatory networks because of its capacity for fine regulation of promoters.

The overall structure of TetR can be broken down into two DNA-binding domains (one per monomer) and a regulatory core, which is responsible for tetracycline recognition and dimerization.

)[citation needed] The DNA-binding domains of TetR recognize a 15 base pair palindromic sequence of the TetA operator.

[1][5] These domains mainly consist of a helix-turn-helix (HTH) motif that is common in TetR protein family members (see below).

[citation needed] TetR protein family members are mostly transcriptional repressors, meaning that they prevent the expression of certain genes at the DNA level.

These proteins can act on genes with various functions including antibiotic resistance, biosynthesis and metabolism, bacterial pathogenesis, and response to cell stress.

TetR as a homodimer: Each monomer is shown in purple or salmon. The helix-turn-helix motif is shown in deep red.
Tetracycline-magnesium complex (blue) bound to cavity of TetR (green). HTH motif shown in pink -note conformational change.
TetR (purple and salmon) in complex with its target DNA sequence. HTH motifs are shown in red binding to the major grooves of the DNA. PDB: 1QPI
HTH motif alignment of three TetR family members: MtrR (magenta), SimR (cyan), & AmtR (green)