3D illustration depicting a cross section of the measles virus. The measles virus is a single stranded, RNA virus that infects the respiratory system. Hemagglutinin (yellow) and membrane fusion proteins (blue) are two envelope glycoproteins which allow it to bind and infect a host cell. Matrix proteins (green) surround the coiled RNA strand which is packaged in nucleoproteins (pink). Phosphoproteins (dark blue) and polymerase proteins (orange) are located along the nucleocapsid, and aid in the viral replication process.