VPG-type capping

Initiation of transcription occurs via a protein primer-dependent mechanism. The protein linked in 5'-genomic RNA is called VPg (viral protein genome-linked) and replaces normal capping. In this way, recognition of viral 5' RNA by host antiviral receptors can be bypassed, and in some cases it replaces the cap function initiation of translation.


Enzymatic reaction:
RNA-dependent RNA polymerase (RdRp) attaches one or more nucleotides to a Tyrosine in the target protein through a nucleotidyl-transferase reaction (Nucleotidylylation).

Picornavirus VPG can be removed by cellular TDP2/VPg unlinkase . This would enhance viral replication, but it is not clear why it does not elicit a RIG -like receptors (RLR) antiviral response.