The antiactivator protein ExsD represses the transcriptional activator ExsA. ExsA activates expression of type III secretion system genes. Repression of ExsA by ExsD is relieved by the secretion chaperone ExsC [1].

1: Structural evidence suggests that antiactivator ExsD from Pseudomonas aeruginosa is a DNA binding protein. Bernhards RC, Jing X, Vogelaar NJ, Robinson H, Schubot FD; Protein Sci. 2009;18:503-513. PMID:19235906