N-alpha-acetyltransferase that specifically mediates the acetylation of N-terminal residues of the transmembrane proteins, with a strong preference for N-termini facing the cytosol. Displays N-terminal acetyltransferase activity towards a range of N-terminal sequences including those starting with Met-Lys, Met-Val, Met-Ala and Met-Met. Required for normal chromosomal segregation during anaphase. May also show histone acetyltransferase activity; such results are however unclear in vivo and would require additional experimental evidences. acetyl-CoA + N-terminal L-methionyl-[transmembrane protein] = CoA + H(+) + N-terminal N(alpha)-acetyl-L-methionyl-[transmembrane protein] acetyl-CoA + L-lysyl-[protein] = CoA + H(+) + N(6)-acetyl-L-lysyl-[protein] Monomer and homodimer; monomer in presence of substrate and homodimer in its absence. Probably forms a intramembrane hairpin-like structure in the membrane. Acetylated: autoacetylation is required for optimal acetyltransferase activity. Belongs to the acetyltransferase family. NAA60 subfamily.