Influenza A virus RNA polymerase PA subunit endonuclease domain (PA endonuclease)

The Influenza A virus RNA polymerase PA subunit endonuclease domain is a critical enzymatic component of the viral heterotrimeric RNA-dependent RNA polymerase (RdRp) complex, which also includes the PB1 and PB2 subunits (UniProt: P03433). Located within the N-terminal region of the PA protein, this domain is responsible for cap-snatching, a process where the virus cleaves the 5-capped primers from host cellular pre-mRNAs to initiate its own viral mRNA transcription. Because this endonuclease activity is essential for viral replication and is highly conserved across various influenza strains, it serves as a potent therapeutic target. Drugs like Baloxavir marboxil specifically bind to the active site of this domain, which contains divalent metal ions (typically manganese or magnesium), thereby blocking the cleavage of host RNA and halting viral protein synthesis (PubMed: 30304651). This mechanism is distinct from neuraminidase inhibitors, providing an alternative for treating influenza, including strains resistant to older antivirals. However, the clinical utility of targeting this domain is challenged by the emergence of specific amino acid substitutions, such as I38T, which significantly reduce drug susceptibility (FDA Label: Xofluza). Monitoring these biomarkers is essential for managing patient treatment and tracking resistance trends. Overall, the PA endonuclease domain represents a distinct and effective site for therapeutic intervention compared to traditional neuraminidase inhibitors.

Other names

PA-NterPA-NPA endonuclease domainPolymerase acidic protein N-terminal domainCap-dependent endonuclease

Inhibition of the cap-dependent endonuclease activity within the PA subunit of the viral RNA polymerase complex, preventing the cleavage of host pre-mRNA capped primers required for viral mRNA synthesis.