SARS (severe acute respiratory syndrome) is caused by a human coronavirus. Human coronaviruses are the major cause of upper respiratory tract illness, such as the common cold, in humans. Coronaviruses are positive-stranded RNA viruses, featuring the largest viral RNA genomes known to date (27-31 kb). The complete sequence of the SARS virus release the coronavirus contains 25 open reading frames. SARS-m is a membrane (M) protein which plays a the key player in virion assembly. One of its functions is to mediate the incorporation of the spikes into the viral envelope.