Figure 4.

The nascent polypeptide-associated complex (NAC) in eukaryotes. (A) Schematic representation of the linear domain organization of human αNAC and βNAC. Both subunits contain a homologous NAC dimerization domain. A conserved positively charged ribosome-binding motif (RRKKK) is located in the amino-terminal domain of βNAC. A conserved ubiquitin-associated domain (UBA) is located at the very carboxyl terminus of αNAC. (B) Crystal structure of the human NAC dimerization domain, which forms a compact β-barrel-like structure (blue, βNAC; violet, αNAC, PDB: 3MCB). The structure of the UBA domain (from archaeal NAC, PDB: 1TR8) consists of a typical three-helix-bundle. Gray dashed lines indicate parts of NAC that are not structurally resolved yet. (C) Surface rendering of yeast 60S (gray) and 40S (wheat) subunits with potential major contact points of NAC near the tunnel exit revealed by cross-linking experiments. βNAC cross-links to both uL23 and eL31, whereas αNAC cross-links to uL29.