FrmR is a formaldehyde sensor  and a member of the CsoR/RcnR family of transcriptional repressors . It was first identified by Herring and Blattner (2004) as a negative regulator of the frmRAB operon; its function can be inactivated by suppression of its amber stop codon .
frmR expression is induced by formaldehyde, but not by S-nitrosoglutathione . Expression of frmR is induced 41-fold upon exposure of cells to the biocide polyhexamethylene biguanide. Overexpression of frmR has no effect on the MIC of polyhexamethylene biguanide .
Based on in vivo and in vitro experiments, it was shown that FrmR senses the toxic chemical formaldehyde directly, with no metal dependence, via the formation of intersubunit methylene bridges between adjacent Pro2 and Cys35 residues .
The X-ray structure of the formaldehyde-treated FrmR tetramer has been identified at 2.7-Å resolution .
FrmR is conserved among the Proteobacteria .
FrmR: "formaldehyde-induced regulator" .
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