ABSTRACT
Influenza virus is a negative strand RNA virus with a segmented genome. Essentially all the studies of the transcription and replication of influenza virus have been carried out with A strain viruses, which contain eight virion RNA (vRNA) segments. With influenza virus, there are eight vRNA templates, all of which have termination signals at their 5' ends rather than their 3' ends. A significant part of the control mechanisms in influenza virus-infected cells is directed at the preferential synthesis of the NP and NS1 proteins early and at delaying the synthesis of the the matrix (M1) protein. The nucleocapsid (NP) and nonstructural protein 1 (NS1) proteins are synthesized early presumably because they are needed for template RNA and/or vRNA synthesis. With regard to the switch from viral mRNA to template RNA synthesis, it is known that the NP protein is required for antitermination and that this protein can only act on transcripts that are initiated without a capped RNA primer.
