NAA40 is an N-alpha-acetyltransferase that specifically mediates the acetylation of the N-terminal residues of histones H4 and H2A [, ]. It has a very specific selectivity for histones H4 and H2A N-termini and specifically recognizes the 'Ser-Gly-Arg-Gly sequence' []. It is conserved from yeast to human. Its budding yeast homologue is known as Nat4 [].