Replication Cycle of Influenza Viruses

Abstract

Each of the genomic segments and the encoded proteins of influenza virus have some role in its replication. Various host factors have been described that are involved at various stages of influenza virus replication. The influenza A virus enters into the host cell by receptor mediated endocytosis. The HA of human and avian influenza viruses bind with sialic acid receptors with α-2, 6 linkage and α-2, 3 linkage, respectively. Both types of receptors are present in pigs. The fusion of the viral envelope with endosomal membrane leads to release of the genomic segments of influenza virus into the cytoplasm of the host cell. ‘Cap snatching’ and ‘stuttering’ are some of the unique phenomena in the replication cycle of influenza virus. The virus produces mRNAs, cRNAs and vRNAs during the course of its replication. The nuclear localization signals (NLSs) located on all the protein constituents, viz. PA, PB1, PB2, NP of the RNP complex are required for the entry of RNPs into the nucleus. The export of the newly formed vRNPs from the nucleus, for further virus assembly at the host cell membrane, is mediated by nuclear export signal (NES) carrying M1 and NEP proteins of influenza virus. The M2 has a pivotal role in the formation of viral particles while the M1 is required during assembly and budding off of the viral particle. The NA and NP proteins also play a role in assembly and release.