Gene expression of influenza viruses during replication

Both transcription and replication of influenza virus genome take place in the nucleus of the infected cells. Initiation of mRNA synthesis requires the generation of capped primers cleaved from the 5' end of the host pre-mRNA by a cap-snatching mechanism. These transcripts are polyadenylated at their 3' ends when the viral polymerase stutters over a polyuridine stretch that is found 15-22 nucleotides from the 5' end of the vRNA. Replication of the viral genome is achieved through primer-independent synthesis of a full-length, positive-sense replicative intermediate, cRNA, that is copied into vRNA. The switch from mRNA to template RNA(cRNA) synthesis requires antitermination activity of NP proteins not associated with nucleocapsids. M gene expression differs among influenza A, B and C viruses.