Cap snatching

The first step of transcription for some negative, single-stranded RNA viruses is cap snatching, in which the first 10 to 20 residues of a host cell RNA are removed (snatched) and used as the 5′ cap and primer to initiate the synthesis of the nascent viral mRNA.^[1] The viral RNA-dependent RNA polymerase (RdRp) can then proceed to transcribe positive-sense viral mRNA using the negative-sense viral RNA as a template. Cap-snatching also explains why some viral mRNA have 5’ terminal extensions of 10-20 nucleotides that are not encoded for in the genome. Examples of viruses that engage in cap-snatching include influenza viruses (Orthomyxoviridae), Lassa virus (Arenaviridae), hantaan virus (Hantaviridae) and rift valley fever virus (Phenuiviridae). Most viruses snatch 15-20 nucleotides except for the families Arenaviridae and Nairoviridae and the genus Thogotovirus (Orthomyxoviridae) which use a shorter strand.^[2]

In the influenza virus, cap snatching occurs in the nucleus of the cell. The cap snatching endonuclease function is contained in the PA subunit of the RNA polymerase.^[3]

In Arenaviridae and Bunyavirales, cap-snatching takes place in the cytoplasm.^[4]