This is a bifunctional membrane/RNA-binding protein that mediates the encapsidation of nucleoprotein cores into the membrane envelope.

[citation needed] It also has multiple regulatory functions, performed by interaction with the components of the host cell.

The mechanisms regulated include a role in the export of the viral ribonucleoproteins from the host cell nucleus, inhibition of viral transcription, and a role in the virus assembly and budding.

[citation needed] The M1 protein forms a layer under the patches of host cell membrane that are rich with the viral hemagglutinin, neuraminidase and M2 transmembrane proteins, and facilitates budding of the mature viruses.

[citation needed] M1 consists of two domains connected by a linker sequence.