This domain is found at the C terminus of the mRNA capping enzyme. The mRNA capping enzyme in yeasts is composed of two separate chains: alpha a mRNA
guanyltransferase and beta an RNA 5'-triphosphate. X-ray crystallography reveals a large
conformational change during guanyl transfer by mRNA capping enzymes [1].
Binding of the enzyme to nucleotides is specific to the GMP moiety of GTP. The viral
mRNA capping enzyme is a monomer that transfers a GMP cap onto the end of mRNA that
terminates with a 5'-diphosphate tail.
Hakansson K, Wigley DB.
Structure of a complex between a cap analogue and mRNA guanylyl transferase demonstrates the structural chemistry of RNA capping.
Proc. Natl. Acad. Sci. U.S.A. 95 1998 1505-10
[PubMed: 9465045] http://dx.doi.org/10.1073/pnas.95.4.1505