THE AMINO-TERMINAL ONE-3RD OF THE INFLUENZA-VIRUS PA PROTEIN IS RESPONSIBLE FOR THE INDUCTION OF PROTEOLYSIS

We have previously described the fact that the individual expression o f influenza virus PA protein induced a generalized proteolysis (J, J, Sanz-Ezquerro, S, de la Luna, J, Ortin, and A, Nieto, J, Virol, 69:242 0-2426, 1995), In this study, we have further characterized this effec t by mapping the regions of PA protein required and have found by dele tion analysis that the first 247 amino acids are sufficient to bring a bout this activity, PA mutants that were able to decrease the accumula tion levels of coexpressed proteins also presented lower steady-state levels due to a reduction in their half-lives, Furthermore, the PA wil d type produced a decrease in the stationary levels of different PA ve rsions, indicating that is itself a target for its induced proteolytic process, All of the PA proteins that induced proteolysis presented nu clear localization, being the sequences responsible for nuclear transp ort located inside the first 247 amino acids of the molecule, To disti nguish between the regions involved in nuclear localization and those involved in induction of proteolysis, we fused the nuclear localizatio n signal of the simian virus 40 T antigen to the carboxy terminus of t he cytosolic versions of PA, None of the cytosolic PA versions affecte d in the first 247-amino-acid part of PA, which were now located in th e nucleus, were able to induce proteolysis, suggesting that conservati on of a particular conformation in this region of the molecule is requ ired for the effect observed, The fact that all of the PA proteins abl e to induce proteolysis presented nuclear localization, together with the observation that this activity is shared by influenza virus PA pro teins from two different type A viruses, suggests a physiological role for this PA protein activity in viral infection.