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Characterization of a unique protein produced by influenza A virus recovered from a long-term persistent infection
W T Lucas1, P Whitaker-Dowling, C R Kaifer
1Department of Microbiology, Biochemistry and Molecular Biology, University of Pittsburgh, School of Medicine, Pennsylvania 15261.
Abstract:
Virus isolated from a persistent infection initiated in BHK cells with influenza A/WSN/33 (H1N1) produced an unusual pattern of protein synthesis in productive infections of BHK cells: The levels of NP and M1 proteins were slightly reduced compared to an infection with wild-type WSN, while the other proteins (Pb1, Pb2, Pa, HA, NS1, and NS2) were synthesized at very low or undetectable levels. In addition, a new viral protein with an approximate molecular weight of 11 kDa (Pi protein) is made (Frielle et al., Virology 138, 103-117, 1984). When viral RNA was analyzed by the Northern blot technique, a deletion was found in the NS gene segment and in NS1 mRNA; all other RNAs were full-sized. Immunoprecipitation of in vitro translation products demonstrated that the Pi protein reacts specifically with anti-NS1 serum. In addition, the Pi protein, like the NS1 of the parental wild-type virus, accumulated in the nucleus of infected cells. These results indicate that the Pi protein is a mutated form of the NS1 protein encoded by a deleted NS segment and suggest that this mutation may be involved in the expression of the persistent virus phenotype.
Insights
A persistent influenza A virus infection produced a novel Pi protein due to a deletion in the NS gene. This mutated NS1 protein accumulates in the nucleus, potentially driving the persistent infection phenotype.
Area of Science:
- Virology
- Molecular Biology
- Cell Biology
Background:
- Influenza A virus (IAV) infections can establish persistent states in host cells.
- Understanding viral protein synthesis alterations is crucial for deciphering IAV persistence mechanisms.
Purpose of the Study:
- To characterize the protein synthesis profile of an IAV strain isolated from a persistent infection.
- To identify and characterize novel viral proteins associated with IAV persistence.
Main Methods:
- Protein analysis using SDS-PAGE and immunoprecipitation.
- Viral RNA analysis via Northern blotting.
- Immunofluorescence to determine protein localization within infected cells.
Main Results:
- A persistent IAV isolate exhibited reduced NP and M1 protein synthesis and very low levels of other viral proteins.
- A novel 11 kDa protein (Pi protein) was detected, reacting with anti-NS1 serum.
- A deletion in the NS gene segment and NS1 mRNA was identified, correlating with Pi protein production.
- The Pi protein localized to the nucleus, similar to wild-type NS1 protein.
Conclusions:
- The Pi protein is a truncated, mutated form of the NS1 protein, arising from a deleted NS gene segment.
- This NS gene deletion and subsequent Pi protein production are linked to the persistent virus phenotype.