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) (PubMed:30028079, PubMed:29581253). N-terminal acetylation of processed beta- and gamma-actin regulates actin filament depolymerization and elongation (PubMed:29581253). In vivo, preferentially displays N-terminal acetyltransferase activity towards acid N-terminal sequences starting with Asp-Asp-Asp and Glu-Glu-Glu (PubMed:30028079, PubMed:29581253). In vitro, shows high activity towards Met-Asp-Glu-Leu and Met-Asp-Asp-Asp (PubMed:10644992, PubMed:29581307). May act as a tumor suppressor (PubMed:10644992). 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] Strongly expressed in heart and skeletal muscle, followed by brain and pancreas, with weak expression in kidney, liver, and lung and no expression in placenta. Belongs to the acetyltransferase family.