Identification of novel influenza A virus proteins translated from PA mRNA
Yukiko Muramoto1, Takeshi Noda, Eiryo Kawakami
1Division of Virology, Department of Microbiology and Immunology, Institute of Medical Science, University of Tokyo, Tokyo, Japan.
Abstract:
Many replication events are involved in the influenza A virus life cycle, and they are accomplished by different virus proteins with specific functions. However, because the size of the influenza virus genome is limited, the virus uses different mechanisms to express multiple viral proteins from a single gene segment. The M2 and NS2 proteins are produced by splicing, and several novel influenza A virus proteins, such as PB1-F2, PB1-N40, and PA-X, have recently been identified. Here, we identified novel PA-related proteins in influenza A virus-infected cells. These newly identified proteins are translated from the 11th and 13th 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 11th and 13th 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.
Insights
Novel N-terminally truncated PA proteins, PA-N155 and PA-N182, were identified in influenza A virus replication. These proteins are crucial for efficient viral replication and pathogenicity in mice.
Area of Science:
- Virology
- Molecular Biology
- Genetics
Background:
- Influenza A virus (IAV) utilizes complex mechanisms to express multiple proteins from limited genome segments.
- Known examples of alternative protein expression include spliced proteins (M2, NS2) and recently identified novel proteins (PB1-F2, PB1-N40, PA-X).
Purpose of the Study:
- To identify and characterize novel PA-related proteins involved in the influenza A virus life cycle.
- To investigate the functional significance of these newly identified proteins in viral replication and pathogenicity.
Main Methods:
- Identification of novel proteins via translation from alternative AUG codons within the PA mRNA sequence.
- Detection of PA-N155 and PA-N182 proteins in cells infected with diverse IAV strains from various hosts.
- Assessment of polymerase activity of N-truncated PAs in conjunction with PB1 and PB2.
- Analysis of replication kinetics and pathogenicity in mice for mutant viruses lacking N-truncated PAs.
Main Results:
- Two novel N-terminally truncated PA proteins, PA-N155 and PA-N182, were identified, translated from the 11th and 13th in-frame AUG codons of PA mRNA.
- These AUG codons are highly conserved, and the proteins were detected across various IAV isolates from different species, indicating universal expression.
- PA-N155 and PA-N182 lack polymerase activity when co-expressed with PB1 and PB2.
- Mutant IAVs lacking these N-truncated PA proteins exhibited slower replication in cell culture and reduced pathogenicity in a mouse model.
Conclusions:
- The study reveals the existence and conservation of novel PA-N155 and PA-N182 proteins in influenza A virus.
- These proteins play a significant role in supporting efficient viral replication and pathogenicity, despite lacking polymerase activity.
- The findings highlight previously unrecognized complexity in influenza A virus protein expression and function.
