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In virology, matrix proteins are structural proteins linking the viral envelope with the virus core.

An example is the M1 protein of the influenza virus, showing affinity to the glycoproteins of the host cell membrane on one side of its molecule and nonspecific affinity for the RNA molecules on its other end, which allows it to form a layer under the membrane, to which the assembled complexes of viral ribonucleoprotein and viral RNA bind and are enveloped and bud out of the cell as new mature viruses.

Viral matrix proteins are responsible for expelling the genetic material once a virus has entered a cell.