N-alpha-acetyltransferase that specifically mediates the acetylation of the N-terminal residues of histones H4 and H2A (By similarity). In contrast to other N-alpha-acetyltransferase, has a very specific selectivity for histones H4 and H2A N-terminus and specifically recognizes the 'Ser-Gly-Arg-Gly sequence' (By similarity). Acts as a negative regulator of apoptosis (By similarity). May play a role in hepatic lipid metabolism (PubMed:22231784). acetyl-CoA + N-terminal L-seryl-[histone H4] = CoA + H(+) + N-terminal N(alpha)-acetyl-L-seryl-[histone H4] acetyl-CoA + N-terminal L-seryl-[histone H2A] = CoA + H(+) + N-terminal N(alpha)-acetyl-L-seryl-[histone H2A] Liver-specific knockout male mice have decreased body mass and are protected from age-associated hepatic steatosis. Male mice show a reduction in the liver triglyceride and free fatty acid levels. No effect on liver cholesterol level, liver weight, and liver function is observed. Belongs to the acetyltransferase family. NAA40 subfamily.