Cholera virulence regulator protein, molecular model. This protein is AphB, a virulence gene activator from the Vibrio cholerae bacterium. It binds to DNA (deoxyribonucleic acid) in its role as a transcriptional regulator. Its structure is a tetramer, with two protein chains (coloured). Cholera is a water-borne bacterial disease that produces a toxin that causes diarrhoea and vomiting.