ABSTRACT The polymerase of the influenza virus is part of the key machinery necessary for viral replication. However, the avian influenza virus polymerase is restricted in mammalian cells. The cellular protein ANP32A has been recently found to interact with viral polymerase, and to both influence polymerase activity and interspecies restriction. Here we report that either ANP32A or ANP32B is indispensable for influenza A virus RNA replication. The contribution of ANP32B is equal to that of ANP32A, and together they play a fundamental role in the activity of mammalian influenza A virus polymerase, while neither human ANP32A nor ANP32B support the activity of avian viral polymerase. Interestingly, we found that avian ANP32B was naturally inactive, leaving ANP32A alone to support viral replication. Two amino acid mutations at sites 129-130 in chicken ANP32B lead to the loss of support of viral replication and weak interaction with the viral polymerase complex, and these amino acids are also crucial in the maintenance of viral polymerase activity in other ANP32 proteins. Our findings strongly support ANP32A&amp;B as key factors for both virus replication and adaption. IMPORTANCE The key host factors involved in the influenza A viral the polymerase activity and RNA replication remain largely unknown. Here we provide evidence that ANP32A and ANP32B from different species are powerful factors in the maintenance of viral polymerase activity. Human ANP32A and ANP32B contribute equally to support human influenza virus RNA replication. However, unlike avian ANP32A, the avian ANP32B is evolutionarily non-functional in supporting viral replication because of a 129-130 site mutation. The 129-130 site plays an important role in ANP32A/B and viral polymerase interaction, therefore determine viral replication, suggesting a novel interface as a potential target for the development of anti-influenza strategies.

Fundamental contribution and host range determination of ANP32 protein family in influenza A virus polymerase activity