Influenza virus binds to receptors on the surface of the host cell via the HA protein. It is internalized into endosomes, after which pH-dependent fusion and uncoating release the viral RNPs into the cytoplasm, where they are transported into the nucleus for replication. Viral messenger RNAs are exported out of the nucleus for protein synthesis, and some of the resulting proteins are transported back into the nucleus to assist in replication and RNP assembly. New RNPs assemble with other virus proteins at the M1 matrix to form virions, which bud from the plasma membrane.