Mutagenic analysis of the 5 ' arm of the influenza A virus virion RNA promoter defines the sequence requirements for endonuclease activity

Short synthetic influenza virus-like RNAs derived from influenza virus prom oter sequences were examined for their ability to stimulate the endonucleas e activity of recombinant influenza virus polymerase complexes in vitro, an activity that is required for the cap-snatching activity of primers from h ost pre-mRNA. An extensive set of point mutants of the 5' arm of the influe nza A virus viral RNA (vRNA) was constructed to determine the cis-acting el ements which influenced endonuclease activity. Activity was found to be dep endent on three features of the conserved vRNA termini: (i) the presence of the 5' hairpin loop structure, (ii) the identity of residues at positions 5 and 10 bases from the 5' terminus, and (iii) the presence of base pair in teractions between the 5' and 3' segment ends. Further experiments discount ed a role for the vRNA U track in endonuclease activation. This study repre sents the first mutagenic analysis of the influenza virus promoter with reg ard to endonuclease activity.