The Influenza virus matrix protein 1 (M1) is a matrix protein of the influenza virus. M1 protein has been shown to play a crucial role in virus replication, assembly, and budding. It forms a coat inside the viral envelope. This is a bifunctional membrane/RNA-binding protein that mediates the encapsidation of RNA-nucleoprotein cores into the membrane envelope. M1 consists of two domains connected by a linker sequence. The N-terminal domain has a multi-helical structure. The C-terminal domain also contains an alpha-helical structure. The M1 protein is the most abundant structural protein in influenza A virus particles. M1 protein of the influenza A virus plays multiple roles in virion assembly and infection. M1 protein was a candidate antigen for a broad-spectrum influenza virus vaccine and the adjuvant chitosan significantly improved the efficacy of the M1 vaccine.