Catalytic subunit of the N-terminal acetyltransferase C (NatC) complex. Catalyzes acetylation of the N-terminal methionine residues of peptides beginning with Met-Leu-Ala and Met-Leu-Gly. Necessary for the lysosomal localization and function of ARL8B sugeesting that ARL8B is a NatC substrate. acetyl-CoA + N-terminal L-methionyl-L-leucyl-[protein] = CoA + H(+) + N-terminal N(alpha)-acetyl-L-methionyl-L-leucyl-[protein] acetyl-CoA + N-terminal L-methionyl-L-isoleucyl-[protein] = CoA + H(+) + N-terminal N(alpha)-acetyl-L-methionyl-L-isoleucyl-[protein] acetyl-CoA + N-terminal L-methionyl-L-phenylalanyl-[protein] = CoA + H(+) + N-terminal N(alpha)-acetyl-L-methionyl-L-phenylalanyl-[protein] acetyl-CoA + N-terminal L-methionyl-L-tryptophyl-[protein] = CoA + H(+) + N-terminal N(alpha)-acetyl-L-methionyl-L-tryptophyl-[protein] acetyl-CoA + N-terminal L-methionyl-L-tyrosyl-[protein] = CoA + H(+) + N-terminal N(alpha)-acetyl-L-methionyl-L-tyrosyl-[protein] Component of the N-terminal acetyltransferase C (NatC) complex. Belongs to the acetyltransferase family. MAK3 subfamily.