UC San Diego

The Influenza A virus (IAV) is a pathogen with a long-standing history of seasonal spread across human communities. Infection by IAV can cause upper respiratory distress in humans that can be fatal especially for those with weakened immune systems. The reservoirs of IAV in animals as well as the rapid mutation rate makes IAV challenging to prevent and eradicate, therefore more understanding of its mechanisms of hijacking host cellular machinery is required to find new solutions for treating this disease. Results from the field suggests that Influenza RNA are acted upon by translation factors in the same manner as host mRNA. Capped and poly (A) tailed viral mRNA are recognized by eIF4E at the 5’ end and PABP1 at the 3’ end to recruit the subsequent initiation factors until the ribosome is assembled and can commence translation. This mechanism of translation initiation however, fails to explain why viral proteins are synthesized to such a high degree. We set out to study the role PABP1 plays on IAV RNA due to it being targeted by the IAV protein NS1. Using qualitative and quantitative binding assays we have further characterized the PABP1-NS1 interaction by discovering that it occurs in the absence of Poly(A). This suggests that NS1 acts upon PABP1 independent of PABP1 binding to a poly(A) tail. Furthermore, we discovered a novel interaction that PABP1 has to the 5’ UTR regions of viral mRNAs. The differences in binding affinity correlate with the protein production measured for those segments. We thus tested the validity of these observations by studying the benefits of IAV 5’ UTRs in a cell free in vitro translation system where cap dependent translation was inhibited. We found that RNAs driven with the viral 5’ UTRs are more resistant to suppression of cap-dependent translation than RNAs driven by a eukaryotic 5’ UTR. To follow up on our in vitro results, we pulled down PABP1 from IAV infected cells and found via RT-qPCR that the 5’ UTRs of IAV RNAs are enriched post pulldown. This suggests that IAV mRNA translation can be initiated by PABP1 acting on the 5’ end.