(I)nteraction of influenza virus NS1 protein and the human homologue of Staufen in vivo and in vitro

A screening for human proteins capable of interacting with influenza virus NS1 has been carried out using the two-hybrid genetic trap in yeast. A cDNA corresponding to the human homologue of Drosophila melanogaster Staufen pr otein (hStaufen) was isolated that fulfilled all genetic controls of the tw o-hybrid protocol. Using a hStaufen cDNA isolated from a lambda human libra ry, the interaction of hStaufen and NS1 proteins was characterised in vivo and in vitro. Co-transfection of NS1 cDNA and a partial cDNA of hStaufen le d to the relocalisation of recombinant hStaufen protein from its normal acc umulation site in the cytoplasm to the nuclear location of NS1 protein. NS1 and hStaufen proteins could be co-immunoprecipitated from extracts of co-t ransfected cells and from mixtures of extracts containing either protein, a s well as from extracts of influenza virus-infected cells, Furthermore, bot h proteins co-localised in the ribosomal and polysomal fractions of influen za virus-infected cells. The interaction was also detected in pull-down exp eriments using a resin containing purified hStaufen and NS1 protein transla ted in vitro, Deletion mapping of the NS1 gene indicated that a mutant prot ein containing the N-terminal 81 amino acids is unable to interact with hSt aufen, in spite of retaining full RNA-binding capacity. These results are d iscussed in relation to the possible mechanisms of action of hStaufen and i ts relevance for influenza virus infection.