AN AMINO-TERMINAL POLYPEPTIDE FRAGMENT OF THE INFLUENZA-VIRUS NS1 PROTEIN POSSESSES SPECIFIC RNA-BINDING ACTIVITY AND LARGELY HELICAL BACKBONE STRUCTURE

The NS1 protein of influenza A virus has the unique property of bindin g to three apparently different RNAs: poly A; a stem-bulge in Us small nuclear RNA; and double-stranded RNA. One of our major goals is to de termine how the NS1 protein recognizes and binds to its several RNA ta rgets. As the first step for conducting structural studies, we have su cceeded in identifying a fragment of the NS1 protein that possesses al l the RNA-binding activities of the full-length protein. The RNA-bindi ng fragment consists of the 73 amino-terminal amino acids of the prote in. We have developed procedures for obtaining large amounts of the po lypeptide in pure form. This has enabled us to establish the RNA-bindi ng properties of this polypeptide and to demonstrate that it retains t he ability to dimerize exhibited by the full-length protein. In additi on, far-UV CD spectroscopy indicates that this RNA-binding polypeptide is largely (approximately 80 %) helical, suggesting that the mode of dimerization of the NS1 protein and of its interaction with RNA is med iated, at least in part, by helices.