The disease cholera results from infection of the epithelial cells of the gut by the phage Vibrio cholerae. The phage-infected cells produce new proteins, cholera toxin A and cholera toxin B, that are secreted into the gut. Cholera toxin B assembles into multisubunit complexes in the membranes of gut epithelial cells and permits cholera toxin A to enter these cells, causing an ion imbalance and massive, watery diarrhea which permits the phage to spread to a new host. The multisubunit complexes formed by cholera toxin B are an example of