Adds a myristoyl group to the N-terminal glycine residue of certain cellular and viral proteins (PubMed:25255805, PubMed:9506952). Also able to mediate N-terminal lysine myristoylation of proteins: catalyzes myristoylation of ARF6 on both 'Gly-2' and 'Lys-3' (PubMed:32103017). Lysine myristoylation is required to maintain ARF6 on membranes during the GTPase cycle (PubMed:32103017). 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] Belongs to the NMT family. Sequence AAF36406.2 was incorrectly indicated as originating from bovine.