Novel influenza A virus proteins translated from PA mRNA

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I identified novel PA-related proteins in influenza A virus-infected cells. These proteins are translated from the eleventh and thirteenth in-frame AUG codons in the PA mRNA and are, therefore, N-terminally truncated forms of PA, which we named PA-N155 and PA-N182, respectively. The eleventh and thirteenth AUG codons are highly conserved among influenza A viruses, and the PA-N155 and PA-N182 proteins were detected in cells infected with various influenza A viruses isolated from different host species, suggesting the expression of these N-truncated PAs is universal in nature among influenza A viruses. These N-truncated PAs did not show polymerase activity when expressed together with PB1 and PB2; however, mutant viruses lacking the N-truncated PAs replicated more slowly in cell culture and had lower pathogenicity in mice than did wild-type virus. These results suggest that these novel PA-related proteins likely possess important functions in the replication cycle of influenza A virus.