Influenza virus polymerase basic protein 2 (PB2) is a core subunit of the viral RNA-dependent RNA polymerase complex that is essential for both transcription and replication of the negative-strand RNA genome. PB2 binds capped host pre-mRNAs and participates in the âÂÂcap snatchingâ process that generates primers for viral mRNA synthesis. PB2 also acts as a key determinant of host range and pathogenicity in different influenza A strains, including through amino-acid substitutions such as the lysine at position 627. In addition, PB2 is imported into the mitochondrial matrix, where it may influence viral replication and hostâÂÂvirus interactions.