Auxillary subunit of the N-terminal acetyltransferase A (NatA) complex which displays alpha (N-terminal) acetyltransferase activity. The NAT activity may be important for vascular, hematopoietic and neuronal growth and development. Required to control retinal neovascularization in adult ocular endothelial cells. In complex with XRCC6 and XRCC5 (Ku80), up-regulates transcription from the osteocalcin promoter (By similarity). Component of the N-terminal acetyltransferase A (NatA) complex composed of NAA10 or probably NAA11 and NAA15 (By similarity). Interacts with XRCC6, NAA50 and XRCC5 (By similarity). Associates with HYPK when in a complex with NAA10 (By similarity). Interaction with HYPK reduces the capacity to interact with NAA50 (By similarity). Mainly cytoplasmic, nuclear in some cases. Cleaved by caspases during apoptosis.