This enzyme belongs to the family of transferases, specifically those transferring phosphorus-containing nucleotide groups (nucleotidyltransferases).op The systematic name of this enzyme class is GTP:mRNA guanylyltransferase. Other names in common use include mRNA capping enzyme, messenger RNA guanylyltransferase, and Protein 2.
Groner Y, Gilboa E, Aviv H (1978). "Methylation and capping of RNA polymerase II primary transcripts by HeLa nuclear homogenates". Biochemistry. 17 (6): 977–82. doi:10.1021/bi00599a005. PMID629955.