Influenza virus natural sequence heterogeneity in segment 8 affects interactions with cellular RNA-binding proteins and splicing efficiency

Segment 8 mRNAs of influenza virus A/Brevig Misson/1918/1 (H1N1) are poorly spliced compared to segment 8 mRNAs of influenza virus A/Netherlands/178/95 (H3N2). Using oligonucleotide-mediated protein pull down with oligos spanning the entire length of segment 8 of either influenza virus H1N1 or influenza virus H3N2 we identified cellular RNA binding proteins that interacted with oligonucleotides derived from either H1N1 or H3N2 sequences. When the identified hot spots for RNA binding proteins in H1N1 segment 8 mRNAs were replaced by H3N2 sequences, splicing efficiency increased significantly. Replacing as few as three nucleotides of the H1N1 mRNA with sequences from H3N2 mRNA, enhanced splicing of the H1N1 mRNAs. Cellular proteins U2AF65 and HuR interacted preferentially with the 3′-splice site of H3N2 and overexpression of HuR reduced the levels of unspliced H1N1 mRNAs, suggesting that U2AF65 and HuR contribute to control of influenza virus mRNA splicing.