title: The novel influenza A virus protein PA-X and its naturally deleted variant show different enzymatic properties in comparison to the viral endonuclease PA.
abstract: The PA protein of Influenza A virus (IAV) encoded by segment 3 acts as a specialized RNA endonuclease in the transcription of the viral genome. The same genomic segment encodes for a second shorter protein, termed PA-X, with the first 191 N-terminal aminoacids (aa) identical to PA, but with a completely different C-ter domain of 61 aa, due to a ribosomal frameshifting. In addition, it has been shown that several IAV isolates encode for a naturally truncated PA-X variant, PAXΔC20, missing the last 20 aa. The biochemical properties of PA-X and PAXΔC20 have been poorly investigated so far. Here, we have carried out an enzymatic characterization of PA-X and its naturally deleted form, in comparison with PA from the human IAV strain A/WSN/33 (H1N1). Our results showed, to the best of our knowledge for the first time, that PA-X possesses an endonucleolytic activity. Both PA and PA-X preferentially cut single stranded RNA regions, but with some differences. In addition, we showed that PAXΔC20 has severely reduced nuclease activity. These results point to a previously undetected role of the last C-ter 20 aa for the catalytic activity of PA-X and support distinct roles for these proteins in the viral life cycle.
authors.affiliation: Institute of Molecular Genetics IGM-CNR, via Abbiategrasso 207, 27100 Pavia, Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Bavagnoli
authors.affiliation: Institute of Molecular Genetics IGM-CNR, via Abbiategrasso 207, 27100 Pavia, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Cucuzza
authors.affiliation: Molecular Virology Unit, Microbiology and Virology Department, Fondazione IRCCS Policlinico San Matteo, P.le Golgi 2, 27100 Pavia, Italy.
authors.forename: Giulia
authors.initials: G
authors.lastname: Campanini
authors.affiliation: Molecular Virology Unit, Microbiology and Virology Department, Fondazione IRCCS Policlinico San Matteo, P.le Golgi 2, 27100 Pavia, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Rovida
authors.affiliation: Molecular Virology Unit, Microbiology and Virology Department, Fondazione IRCCS Policlinico San Matteo, P.le Golgi 2, 27100 Pavia, Italy.
authors.forename: Stefania
authors.initials: S
authors.lastname: Paolucci
authors.affiliation: Molecular Virology Unit, Microbiology and Virology Department, Fondazione IRCCS Policlinico San Matteo, P.le Golgi 2, 27100 Pavia, Italy.
authors.forename: Fausto
authors.initials: F
authors.lastname: Baldanti
authors.affiliation: Institute of Molecular Genetics IGM-CNR, via Abbiategrasso 207, 27100 Pavia, Italy maga@igm.cnr.it.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Maga
mesh_terms: D003067:Coenzymes / Q000378:metabolism; D004722:Endoribonucleases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D053118:Influenza A Virus, H1N1 Subtype / Q000201:enzymology*; D009690:Nucleic Acid Conformation; D012313:RNA / Q000737:chemistry / Q000378:metabolism; D059367:RNA Cleavage; D012324:RNA-Dependent RNA Polymerase / Q000378:metabolism*; D012097:Repressor Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D017384:Sequence Deletion; D017361:Viral Nonstructural Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D014764:Viral Proteins / Q000378:metabolism*
chemical_list: D003067:Coenzymes; C061290:PA protein, influenza viruses; C573926:PA-X protein, influenza A virus; D012097:Repressor Proteins; D017361:Viral Nonstructural Proteins; D014764:Viral Proteins; D012313:RNA; D012324:RNA-Dependent RNA Polymerase; D004722:Endoribonucleases