RNA structure interactions and ribonucleoprotein processes of the influenza A virus

Dawson, Wayne K; Lazniewski, Michal; Plewczynski, Dariusz

Transcription (viral mRNA production) is required to generate new copies of the viral proteins for creating a new virion. Several additional editing steps must be done before a viable mRNA can be exported and translated; the mRNA must have a properly constructed 5 0 -end on the nucleic acid sequence, a cap with a 5 0 untranslated region (5 0 -UTR) and a poly-adenylated [poly(A)] tract inserted at the 3 0 -end of the sequence. The viral polymerase catalyzes not only RNA transcription but also cleaves the host cell's mRNA and splices it onto the forming viral mRNA using cap-snatching by way of the PA and PB2 subunits [21] . To do this, the host Pol II and resident spliceosome factors become involved in this transcription process. For example, although M1 is translated from the unspliced mRNA, both M2 and M42 are the spliced variants. Similarly, NS1 is the unspliced version, while the NEP (NS2) is the spliced variant [44] . Additional known splice variants that have been identified in the viral genome are listed in Table 1 . The Pol II is also captured to recruit its capping machinery, which provides the required cap and 13 nt primer sequence at the 5 0 -end of the viral transcript using PA and PB2 (a process shown as the second and third steps from the top in Figure 1 ). The mimicry must be complete, so that the viral mRNA is processed in the same way as the host's mRNA. Midway along the vRNA sequence in Figure 1 (middle), one can see an image of various splice factors that introduce the possibility of alternative splicing in the transcription. Just like the host's own mRNA, by the end of this process, the viral mRNA is probably coated with the host's exonjunction-core proteins and associated interacting proteins, the cap-binding complex, poly(A) binding proteins and most likely other important proteins needed for export to the cytosol and translation into proteins by the host's ribosomal RNA [77] .