RBM6-mediated alternative splicing facilitates the adaptation of Eurasian avian-like H1N1 swine influenza virus

The Eurasian avian□like (EA) H1N1 swine influenza virus (SIV), derived from avian influenza viruses (AIV), poses a serious threat to public health due to its capacity for cross□species transmission and pandemic emergence. The molecular determinants underlying its replication advantage over AIV remain poorly defined. Here, we identify RNA□binding motif protein 6 (RBM6) as a novel host factor that differentially regulates the replication of EA H1N1 SIV and AIV. Mechanistically, RBM6 binds to the critical M901 site of the viral M segment, thereby modulating RNA splicing. Substitution of M901C with M901T markedly reduced RBM6 binding, impaired M segment splicing, and attenuated viral replication both in vitro and in vivo . Conservation analysis revealed that M901T is common in avian strains, whereas M901C is predominantly maintained in swine strains, underscoring M901C as a determinant of swine adaptation. Complementation experiments further demonstrated that swine RBM6, but not avian RBM6, restored EA H1N1 SIV replication. Taken together, our findings uncover a previously unrecognized role of RBM6 in shaping influenza virus replication and highlight the RBM6-M901C axis may serve as potential targets for controlling influenza virus adaptation and interspecies transmission.