NUCLEUS-TARGETING DOMAIN OF THE MATRIX PROTEIN (M(1)) OF INFLUENZA-VIRUS

The matrix protein M(1) of influenza virus A/WSN/33 was shown by immunofluorescent staining to be transported into the nuclei of transfected cells without requiring other viral proteins. We postulated the existence of a potential signal sequence at amino acids 101 to 105 (RKLKR) that is required for nuclear localization of the M(1) protein. When CV1 cells were transfected with recombinant vectors expressing the entire M(1) protein (amino acids 1 to 252) or just the first 112 N-terminal amino acids, both the complete M(1) protein and the truncated M(1) protein were transported to the nucleus. In contrast, expression in CVI cells of vectors coding for M(1) proteins with deletions from amino acids 77 to 202 or amino acids 1 to 134 resulted only in cytoplasmic immunofluorescent staining of these truncated M(1) proteins without protein being transported to the nucleus. Moreover, no nuclear membrane translocation occurred when CV1 cells were transfected with recombinant vectors expressing M(1) proteins with deletions of amino acids 101 to 105 or with substitution at amino acids 101 to 105 of SNLNS for RKLKR Furthermore, a synthetic oligopeptide corresponding to M(1) protein amino acids 90 to 108 was also transported into isolated nuclei derived from CV1 cells, whereas oligopeptides corresponding to amino acid sequences 25 to 40, 67 to 81, and 135 to 164 were not transported into the isolated cell nuclei. These data suggest that the amino acid sequence (101)RKLKR(105) is the nuclear localization signal of the M(1) protein.