Plant UBX Domain-containing Protein 1, PUX1, Regulates the Oligomeric Structure and Activity of Arabidopsis CDC48

p97/CDC48 is a highly abundant hexameric AAA-ATPase that functions as a molecular chaperone in numerous diverse cellular activities. We have identified an Arabidopsis UBX domain-containing protein, PUX1, which functions to regulate the oligomeric structure of the Arabidopsis homolog of p97/CDC48, AtCDC48, as well as mammalian p97. PUX1 is a soluble protein that co-fractionates with non-hexameric AtCDC48 and physically interacts with AtCDC48 in vivo. Binding of PUX1 to AtCDC48 is mediated through the UBX-containing C-terminal domain. However, disassembly of the chaperone is dependent upon the N-terminal domain of PUX1. These findings provide evidence that the assembly and disassembly of the hexameric p97/CDC48 complex is a dynamic process. This new unexpected level of regulation for p97/CDC48 was demonstrated to be critical in vivo as pux1 loss-of-function mutants display accelerated growth relative to wild-type plants. These results suggest a role for AtCDC48 and PUX1 in regulating plant growth.