Doa1 Is a Cdc48 Adapter That Possesses a Novel Ubiquitin Binding Domain

Cdc48 (p97/VCP) is a AAA‐ATPase molecular chaperone whose cellular functions are facilitated by its interaction with ubiquitin binding cofactors (e.g. Npl4‐Ufd1 and Shp1). Several studies have provided evidence that yeast Doa1 (Ufd3/Zzz4) and its mammalian homolog, PLAA, interact with Cdc48/p97/VCP. However, a direct interaction has never been shown nor has the physiological significance of this interaction been determined. Herein, we demonstrate a direct physical interaction between Cdc48 and the PUL domain of Doa1. We find that Doa1 possesses a novel ubiquitin binding domain (a PFU domain: PLAA Family Ubiquitin binding domain), allowing it to act as a ubiquitin‐binding adapter of Cdc48. We uncover a genetic link between Doa1 and Cdc48 that suggests involvement of Doa1 in Cdc48‐mediated processes. Lastly, we provide evidence of functional conservation within the PLAA family by showing that a human‐yeast chimera binds to ubiquitin and complements doa1Ä phenotypes in yeast. Combined, our data suggest that Doa1 plays a physiological role as a ubiquitin binding cofactor of Cdc48, and allow us to speculate that human PLAA plays an analogous role via its interaction with p97/VCP. This work was supported by a postdoctoral fellowship from the American Heart Association and NIH Grant R01‐GM30308.