Represses transcription of the icaADBC operon necessary for biofilm production. Homodimer. Cells display an increase of ica transcription of about 100-fold, and poly-N-acetylglucosamine polysaccharide (PNAG) synthesis about 10-fold. Adherence to polystyrene microtiter wells also increases. Double deletion of icaR and tcaR increases ica transcription about 500-fold, and poly-N-acetylglucosamine polysaccharide (PNAG) synthesis about 100-fold. Adherence is significantly greater than that of the single icaR mutant. Binding to the ica operator DNA involves two IcaR dimers and is highly cooperative.