Influenza virus M1 mRNA is translated into the matrix protein M1, whereas the ion channel protein M2 is produced after the splicing of M1 mRNA into M2 mRNA. Mor et al. now show that M1 mRNA and M2 mRNA accumulate at nuclear speckles, which are enriched for splicing factors, following transcription. On the basis of their data, they propose a model whereby M1 mRNA is trafficked to nuclear speckles by the viral protein NS1 bound to cellular NS1-BP for hnRNP K-dependent splicing into M2 mRNA and nuclear export. The interaction of SON (a cellular factor that is involved in the assembly of nuclear speckles and alternative splicing) with NS1, NS1-BP, hnRNP K and M1 mRNA further supports the notion that influenza virus subverts nuclear speckles to promote efficient splicing. Finally, nuclear export was shown to be coupled to splicing and to be mediated by cellular export factors. In sum, this study reveals a previously unknown role for NS1 in mRNA targeting to nuclear speckles and splicing.