COMPLEX STRUCTURE OF THE NUCLEAR TRANSLOCATION SIGNAL OF INFLUENZA-VIRUS POLYMERASE PA SUBUNIT

The protein regions involved in the nuclear translocation of the influ enza virus PA polymerase subunit have been identified by deletion anal ysis of the protein expressed from a recombinant simian virus 40. Two regions seem to play a role in the process: region I (amino acids 124 to 139) and region II (amino acids 186 to 247). A nucleoplasmin-like n uclear translocation signal (NLS) has been identified in region I and an additional NLS appears to be present in region II, although no cons ensus targeting sequence can be detected. Alteration in any of the reg ions identified by short deletions completely prevented nuclear transp ort, whereas elimination of the regions I or II by large amino- or car boxy-terminal deletions did not prevent nuclear targeting of the trunc ated protein. In addition, a point mutation at position 154 completely eliminated nuclear transport. A beta-galactosidase fusion protein con taining the 280 amino acid terminal region of the PA protein was parti ally transported to the nucleus and mutant PA proteins with a cytoplas mic phenotype could not be rescued by superinfection with influenza vi rus. These results suggest that the PA protein contains a functional n uclear targeting region which is required in influenza virus infection , with two independent NLSs, one in region I and the other in region I I.