Cap snatching
Cap Snatching[edit | edit source]
Cap snatching is a mechanism used by certain viruses to initiate the synthesis of their own mRNA by hijacking the host cell's transcription machinery. This process is crucial for the replication of many negative-sense RNA viruses, including the Orthomyxoviridae family, which includes the influenza virus.
Mechanism[edit | edit source]
Cap snatching involves the cleavage of the 5' cap structure from host pre-mRNAs. The viral endonuclease enzyme, which is part of the viral RNA polymerase complex, recognizes and binds to the host mRNA. It then cleaves the mRNA a few nucleotides downstream of the cap structure. The resulting capped RNA fragment is used as a primer by the viral RNA polymerase to synthesize viral mRNA.
The cap snatching process allows the virus to efficiently utilize the host's ribosomes for the translation of viral proteins, as the capped viral mRNAs are recognized as host mRNAs by the cellular translation machinery.
Importance in Viral Replication[edit | edit source]
Cap snatching is essential for the replication of viruses that rely on this mechanism. Without the ability to snatch caps, these viruses would be unable to produce the mRNAs necessary for the synthesis of viral proteins, ultimately halting their replication cycle.
The process also provides a means for the virus to evade host immune responses, as the viral mRNAs closely resemble host mRNAs, making it difficult for the host cell to distinguish between self and non-self.
Cap Snatching in Influenza Virus[edit | edit source]
The influenza virus is a well-studied example of a virus that utilizes cap snatching. The viral RNA polymerase complex, composed of the PB1, PB2, and PA proteins, is responsible for this process. The PB2 subunit binds to the cap structure of host pre-mRNAs, while the PA subunit acts as the endonuclease that cleaves the RNA.
The capped RNA fragments are then used by the PB1 subunit to initiate the synthesis of viral mRNA, which is subsequently translated into viral proteins necessary for the assembly of new viral particles.
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