title: Two aromatic residues in the PB2 subunit of influenza A RNA polymerase are crucial for cap binding.
abstract: mRNAs are capped at their 5'-end by a unique cap structure containing N7-methyl guanine. Recognition of the cap structure is of paramount importance in some of the most central processes of gene expression as well as in some viral processes, such as priming of influenza virus transcription. The recent resolution of the structure of three evolutionary unrelated cap binding proteins, the vaccinia viral protein VP39, the eukaryotic translation factor eIF4E, and the nuclear cap-binding protein CBP20 showed that the recognition of the cap structure is achieved by the same general mechanism, i.e. by "sandwiching" of the N7-methyl guanine of the cap structure between two aromatic amino acid residues. The purpose of the present study was to test whether a similar cap recognition mechanism had independently evolved for the RNA polymerase of influenza virus. Combining in vivo and in vitro methods, we characterized two crucial aromatic amino acids, Phe363 and Phe404, in the PB2 subunit of the viral RNA polymerase that are essential for cap binding. The aromaticity of these two residues is conserved in influenza A, B, and C and even in the divergent Thogoto virus PB2 subunits. Thus, our results favor a similar mechanism of cap binding by the influenza RNA polymerase as in the evolutionary unrelated VP39, eIF4E, and CBP20.
authors.affiliation: Sir William Dunn School of Pathology, University of Oxford, South Parks Road, United Kingdom.
authors.forename: Pierre
authors.initials: P
authors.lastname: Fechter
authors.forename: Louise
authors.initials: L
authors.lastname: Mingay
authors.forename: Jane
authors.initials: J
authors.lastname: Sharps
authors.forename: Anna
authors.initials: A
authors.lastname: Chambers
authors.forename: Ervin
authors.initials: E
authors.lastname: Fodor
authors.forename: George G
authors.initials: GG
authors.lastname: Brownlee
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D017931:DNA Primers; D012321:DNA-Directed RNA Polymerases / Q000737:chemistry / Q000378:metabolism*; D005914:Globins / Q000235:genetics; D009980:Influenza A virus / Q000201:enzymology* / Q000235:genetics; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding; D012315:RNA Caps / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D011995:Recombination, Genetic; D017386:Sequence Homology, Amino Acid
chemical_list: D017931:DNA Primers; D012315:RNA Caps; D012333:RNA, Messenger; D005914:Globins; D012321:DNA-Directed RNA Polymerases