Component of several N-terminal acetyltransferase complexes (PubMed:20154145, PubMed:29754825, PubMed:32042062). Inhibits the N- terminal acetylation activity of the N-terminal acetyltransferase NAA10-NAA15 complex (also called the NatA complex) (PubMed:29754825, PubMed:32042062). Has chaperone-like activity preventing polyglutamine (polyQ) aggregation of HTT in neuronal cells probably while associated with the NatA complex (PubMed:17947297, PubMed:20154145). May play a role in the NatA complex-mediated N-terminal acetylation of PCNP (PubMed:20154145). {ECO:0000269|PubMed:17947297, ECO:0000269|PubMed:20154145, ECO:0000269|PubMed:29754825, ECO:0000269|PubMed:32042062}. This is the function of HYPK (huntingtin interacting protein K, ENSG00000242028).