N-alpha-acetyltransferase that specifically mediates the acetylation of the acidic amino terminus of processed forms of beta- and gamma-actin (ACTB and ACTG, respectively). N-terminal acetylation of processed beta- and gamma-actin regulates actin filament depolymerization and elongation. In vivo, preferentially displays N-terminal acetyltransferase activity towards acid N-terminal sequences starting with Asp-Asp-Asp and Glu-Glu-Glu. In vitro, shows high activity towards Met-Asp-Glu-Leu and Met-Asp-Asp-Asp. May act as a tumor suppressor. acetyl-CoA + N-terminal L-aspartyl-L-aspartyl-L-aspartyl-[protein] = CoA + H(+) + N-terminal N-acetyl-L-aspartyl-L-aspartyl-L-aspartyl-[protein] acetyl-CoA + N-terminal L-glutamyl-L-glutamyl-L-glutamyl-[protein] = CoA + H(+) + N-terminal N-acetyl-L-glutamyl-L-glutamyl-L-glutamyl-[protein] Belongs to the acetyltransferase family.