The novel influenza A virus protein PA-X and its naturally deleted variant show different enzymatic properties in comparison to the viral endonuclease PA

Nucleic Acids Res. 2015 Oct 30;43(19):9405-17. doi: 10.1093/nar/gkv926. Epub 2015 Sep 17.

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.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Coenzymes / metabolism
  • Endoribonucleases / antagonists & inhibitors
  • Endoribonucleases / genetics
  • Endoribonucleases / metabolism*
  • Influenza A Virus, H1N1 Subtype / enzymology*
  • Nucleic Acid Conformation
  • RNA / chemistry
  • RNA / metabolism
  • RNA Cleavage
  • RNA-Dependent RNA Polymerase / metabolism*
  • Repressor Proteins / antagonists & inhibitors
  • Repressor Proteins / genetics
  • Repressor Proteins / metabolism*
  • Sequence Deletion
  • Viral Nonstructural Proteins / antagonists & inhibitors
  • Viral Nonstructural Proteins / genetics
  • Viral Nonstructural Proteins / metabolism*
  • Viral Proteins / metabolism*

Substances

  • Coenzymes
  • PA protein, influenza viruses
  • PA-X protein, influenza A virus
  • Repressor Proteins
  • Viral Nonstructural Proteins
  • Viral Proteins
  • RNA
  • RNA-Dependent RNA Polymerase
  • Endoribonucleases