The Multiple Functions of the PAQosome: An R2TP- and URI1 Prefoldin-Based Chaperone Complex

The PAQosome (Particle for Arrangement of Quaternary structure) is a large multisubunit chaperone complex that is essential for the assembly and stabilization of other macromolecular complexes. It also interacts with several chaperones including Hsp90, Hsp70, and CCT. The PAQosome is comprised of the R2TP complex, the URI1 prefoldin complex (also known as the non-canonical prefoldin-like complex), the RNA polymerase subunit RPB5, and the WD40 repeat protein WDR92. The R2TP complex is conserved among eukaryotes and has been comprehensively studied over the last 13 years. The R2TP complex is known for its involvement in the assembly and stabilization of L7Ae ribonucleoproteins, U5 small nuclear ribonucleoprotein, RNA polymerase II, phosphatidylinositol-3-kinase-related proteins (PIKKs), and the tuberous sclerosis complex (TSC1-TSC2). By contrast, the URI1 prefoldin complex has evolved exclusively in higher metazoans. Although the URI1 prefoldin complex was initially reported more than 15 years ago, little is known about its function and its role within the PAQosome. Given that URI1 is overexpressed in many types of cancer, it is surprising that the URI1 prefoldin complex has been overlooked. This chapter provides an update on the recent progress uncovering the physiological roles of each PAQosome subunit and provides an overview of the potential functions of the URI1 prefoldin complex.