The transcription/replication activity of the polymerase of influenza A viruses is not correlated with the level of proteolysis induced by the PA subunit.

The PA subunit of the influenza virus polymerase has been shown to induce degradation of coexpressed proteins, but its role in the replication activity of the polymerase is not fully understood. Here, PA proteins derived from several influenza A viruses were examined at 37 and 33 degrees C for both the level of proteolysis they induced and the efficiency with which they ensured transcription/replication of a viral-like RNA within a polymerase complex reconstituted in vivo from cloned cDNAs. Two mutants of A/Victoria/3/75 PA showed a decreased ability to induce proteolysis as compared to the wild-type PA, but still appeared to be as active as the wild-type protein with respect to the polymerase activity. Furthermore, we observed that the ability of PR8-PA to induce proteolysis was severely impaired at 33 degrees C as compared to 37 degrees C, while the efficiency with which the PR8-derived polymerase complex ensured transcription/replication of the viral-like RNA was similar at both temperatures. Taken together, our observations suggest that the transcription/replication activity of the polymerase of influenza A viruses is not correlated with the level of proteolysis induced by the PA subunit. Copyright 2001 Academic Press.