Catalytic subunit of the NatB complex which catalyzes acetylation of the N-terminal methionine residues of peptides beginning with Met-Asp, Met-Glu, Met-Asn and Met-Gln. Proteins with cell cycle functions are overrepresented in the pool of NatB substrates. Required for maintaining the structure and function of actomyosin fibers and for proper cellular migration. acetyl-CoA + N-terminal L-methionyl-L-asparaginyl-[protein] = CoA + H(+) + N-terminal N(alpha)-acetyl-L-methionyl-L-asparaginyl-[protein] acetyl-CoA + N-terminal L-methionyl-L-glutaminyl-[protein] = CoA + H(+) + N-terminal N(alpha)-acetyl-L-methionyl-L-glutaminyl-[protein] acetyl-CoA + N-terminal L-methionyl-L-aspartyl-[protein] = CoA + H(+) + N-terminal N(alpha)-acetyl-L-methionyl-L-aspartyl-[protein] acetyl-CoA + N-terminal L-methionyl-L-glutamyl-[protein] = CoA + H(+) + N-terminal N(alpha)-acetyl-L-methionyl-L-glutamyl-[protein] Component of the N-terminal acetyltransferase B (NatB) complex which is composed of NAA20 and NAA25. Belongs to the acetyltransferase family. ARD1 subfamily.