Fig. 1. Cdc48 binds the 20S peptidase.

(A) PAN and Cdc48 have distinct N domains but homologous AAA+ modules and HbYX motifs. (B) Examples of archaea in which PAN was absent but 20S and Ccd48 were present. Red Cdc48 tripeptides match HbYX or related sequences. (C) Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed that purified T. acidophilum His₆-Cdc48^EQ/EQ pulled down two proteins from a T. acidophilum cell extract, which were identified as the 20S α and β subunits (Fig. S2). (D) Using purified T. acidophilum proteins, 20S with a His₆-tagged β subunit pulled down roughly stoichiometric quantities of untagged Cdc48^EQ/EQ in the presence of 2 mM ATP but not ADP.