INFLUENZA-VIRUS M1 PROTEIN BINDS TO RNA THROUGH ITS NUCLEAR-LOCALIZATION SIGNAL

The RNA-binding activity of influenza A virus M1 protein was studied b y cross-linking the protein to viral RNA followed by sequence analysis of the oligoribonucleotide bound to the protein as well as sequence a nalysis of the M1 peptide bound to the RNA. M1 was found to bind to RN A without any RNA sequence specificity, as verified in a series of fil ter-binding experiments using a large variety of nucleic acids includi ng DNA. The peptide sequence that bound to the RNA was the RKLKR nucle ar localization signal of M1. Site-specific mutagenesis of recombinant M1 showed that most of the basic residues in that region had to be mu tated in order to inhibit RNA-binding. We also constructed an M1 mutan t that no longer bound to RNA but which was still able to inhibit the in vitro transcription activity of isolated viral ribonucleoprotein, a lbeit to a lower extent. Mutation of the zinc-binding sequence had no effect on RNA-binding or transcription-inhibition activity.