Important for biofilm formation. Represses expression of McbA by binding to its promoter region, which prevents colanic acid overproduction and mucoidy. Induced by LsrR, LsrK, MqsR and TqsA. Repressed by LuxS and YgiV. Disruption of this gene induces 30 genes and represses 10 genes more than fourfold. It decreases biofilm formation, increases extracellular indole, leads to colanic acid overproduction and elicits mucoidy.