Adds a myristoyl group to the N-terminal glycine residue of certain cellular and viral proteins (PubMed:15753093). Also able to mediate N-terminal lysine myristoylation of proteins: catalyzes myristoylation of ARF6 on both 'Gly-2' and 'Lys-3' (By similarity). Lysine myristoylation is required to maintain ARF6 on membranes during the GTPase cycle (By similarity). Required for normal embryogenesis (PubMed:15753093). N-terminal glycyl-[protein] + tetradecanoyl-CoA = CoA + H(+) + N-tetradecanoylglycyl-[protein] N-terminal glycyl-L-lysyl-[protein] + tetradecanoyl-CoA = CoA + H(+) + N-terminal glycyl-(N(6)-tetradecanoyl)-L-lysyl-[protein] Copurifies with ribosomes. Ubiquitous. Complete embryonic lethality. Embryos die between 3.5 and 7.5 dpc. Belongs to the NMT family.