The polymerase of negative stranded RNA viruses

Negative-sense RNA viruses are divided into non segmented viruses such as Ebola and segmented viruses such as influenza. Both groups protect their genomic RNA inside a nucleocapsid protein(NP) that the viral RNA-Dependent RNA polymerase must navigate during transcription and replication. Both classes share similar polymerase core architecture but their capping and structural mechanisms are different. NNS viruses use internal PRNTase and MTase domains to synthesize fully modified 5’ caps and have rigid locked nucleoplasmids. SNS viruses have loosely organized nucleocaspids and hijack host mRNA caps via a cap dependent endonuclease domain. In NNs systems the phosphoprotein (P) is an important cofactor that changes the L proteins structural appendage and acts as a processivity factor whereas SNS polymerases  accesses templates directly. Recent Invitro assays have shown that polymerases can initiate denovo or using primers on naked RNA through precise 3’ terminal base pairing. Also template associated protein NP remains important to achieve full processivity. 
(MCW)