Faustovirus capping enzyme （FCE） catalyzed the addition of N7-methylguanosine cap （m7G） at the triphosphate and diphosphate positions at the 5′ end of the transcription product to produce RNA with Cap-0 cap. FCE is a monosubunit enzyme with three enzyme activities required to add Cap-0 cap structure to RNA: triphosphatase, guanine transferase, and （guanine-N7）-methyltransferase. The addition of Cap-0 cap structure, the first nucleotide 2′-O-methylation （Cap-1） and polyadenylation tailing （poly（A）） are key steps in eukaryotic mRNA maturation. The Cap-0 structure can also increase RNA stability and avoid triphosphorylated RNA activate the natural immune response.
FCE can maintain capping activity from low temperature to high temperature range of 55°C. Generally, 1 μl FCE （25 units） can be capped over 100 μg of RNA in 1 hour at 37°C. This product provides GTP and S-adenosylmethionine （SAM） required for capping activity.