 Many viruses that cause human disease express viroporins, such as hepatitis C virus, HIV-1, influenza A virus, poliovirus, respiratory syncytial virus, and SARS-CoV.Viroporins are usually small - under 100 or 120 amino acid residues - and contain at least one region capable of folding into an amphipathic transmembrane helix.Some examples also contain stretches of basic amino acids, or stretches of aromatic amino acids thought to reside in the interfacial region of the membrane.