Influenza, commonly known as the flu, is a highly contagious viral disease that poses a significant global health burden. At the heart of the influenza virus's ability to cause infection and spread is its polymerase, an enzyme complex that drives the replication of the virus. This article delves into the role and workings of the influenza virus polymerase.
Understanding Influenza Virus Polymerase
The influenza virus belongs to the Orthomyxoviridae family, characterized by a segmented, negative-sense RNA genome. The genome comprises eight segments, each of which encodes one or two proteins. Among these proteins are the three subunits - PA, PB1, and PB2 - that form the viral RNA-dependent RNA polymerase.
The polymerase carries out two key processes in the viral life cycle: transcription (the synthesis of viral mRNA from the viral RNA genome) and replication (the production of new copies of the viral RNA genome).
Transcription Mechanism
Transcription begins with the binding of the polymerase complex to the 5' end of the viral RNA (vRNA). The PB2 subunit recognizes and binds to capped RNA primers derived from host pre-mRNAs, a process known as cap-snatching. These primers serve as the starting point for transcription.
The PB1 subunit, which possesses the polymerase activity, then synthesizes a complementary RNA strand (cRNA) using the vRNA as a template. This cRNA serves as the mRNA, which is translated into viral proteins by the host cell's machinery.
Replication Mechanism
During replication, the polymerase synthesizes a full-length cRNA copy of the vRNA, but this time without a cap or poly-A tail. This cRNA then serves as a template for the synthesis of new vRNA segments.
The newly synthesized vRNA segments are packaged with viral proteins, including the polymerase subunits and the nucleoprotein (NP), into new virus particles. These particles are then released from the cell to infect other cells, perpetuating the viral life cycle.