['A multi-subunit protein complex called cohesin is involved in holding sister chromatids together after DNA replication. Cohesin contains four core subunits: Smc1, Smc3, Scc1, and Scc3. Biochemical studies suggest that Smc1 and Smc3 each form 50 nm-long antiparallel coiled coils (arms) and bind to each other to form V-shaped heterodimers with globular ABC-like ATPases (created by the juxtaposition of N- and C-terminal domains) at their apices. These Smc "heads" are connected by Scc1, creating a tripartite proteinaceous ring.', "To investigate the role of Smc1 and Smc3's ATPase domains, we engineered smc1 and smc3 mutations predicted to abolish either ATP binding or hydrolysis. All mutations abolished Smc protein function. The binding of ATP to Smc1, but not Smc3, was essential for Scc1's association with Smc1/3 heterodimers. In contrast, mutations predicted to prevent hydrolysis of ATP bound to either head abolished cohesin's association with chromatin but not Scc1's ability to connect Smc1's head with that of Smc3. Inactivation of the Scc2/4 complex had a similar if not identical effect; namely, the production of tripartite cohesin rings that cannot associate with chromosomes."] Is aTP hydrolysis required for cohesin 's association with chromosomes?