Nido -type capping

RNAs are capped by a unique viral reaction. These viruses RdRp complex contains an RNA:GDP polyribonucleotidyltransferase (PRNTase) that forms a covalent bond to the 5' end of the viral RNA through a monophosphate group. The enzyme then transfers the 5'-monophosphate RNA to GDP and forms the GpppRNA structure. The RNA is further N7 methylated and 2'O methylated by two other viral enzymes

Recent publications suggest that mRNA synthesis might be directly protein primed, thereby skipping the PRNTase step

(PRNTase=polyribonucleotidyl transferase, RdRp=RNA-dependent RNA polymerase, GTase=guanylyltransferase, MTase=methyltransferase, SAM= S-adenosylmethionine, SAH= S-adenosylhomocysteine)

Enzymatic reaction:
RNA:polyribonucleotidyl transferase (involves covalent link enz-Asn-RNA)
NTPase Rhea 23680
Guanylyltransferase
N7methyltransferase Rhea 65380
2'O methyltransferase : Rhea 67020 PF06460