The ring-shaped ATPase machine, cohesin, regulates sister chromatid cohesion, 
transcription, and DNA repair by topologically entrapping DNA. Here, we propose 
a rigid scaffold model to explain how the cohesin regulators Pds5 and Wapl 
release cohesin from chromosomes. Recent studies have established the Smc3-Scc1 
interface as the DNA exit gate of cohesin, revealed a requirement for ATP 
hydrolysis in ring opening, suggested regulation of the cohesin ATPase activity 
by DNA and Smc3 acetylation, and provided insights into how Pds5 and Wapl open 
this exit gate. We hypothesize that Pds5, Wapl, and SA1/2 form a rigid scaffold 
that docks on Scc1 and anchors the N-terminal domain of Scc1 (Scc1N) to the Smc1 
ATPase head. Relative movements between the Smc1-3 ATPase heads driven by ATP 
and Wapl disrupt the Smc3-Scc1 interface. Pds5 binds the dissociated Scc1N and 
prolongs this open state of cohesin, releasing DNA. We review the evidence 
supporting this model and suggest experiments that can further test its key 
principles.