Auxillary subunit of N-terminal acetyltransferase complexes which display alpha (N-terminal) acetyltransferase (NAT) activity (PubMed:15496142, PubMed:20154145, PubMed:29754825, PubMed:32042062). The NAT activity may be important for vascular, hematopoietic and neuronal growth and development (PubMed:15496142). Required to control retinal neovascularization in adult ocular endothelial cells (PubMed:11687548). In complex with XRCC6 and XRCC5 (Ku80), up-regulates transcription from the osteocalcin promoter (PubMed:12145306).
