A model for Scc2p Stimulation of Cohesin's ATPase and its Inhibition by Acetylation of Smc3p
The evolutionarily conserved cohesin complex mediates sister chromatid cohesion and facilitates mitotic chromosome condensation, DNA repair, and transcription regulation. These biological functions require cohesins two ATPases, formed by the Smc1p and Smc3p subunits. Cohesins ATPase activity is stimulated by the Scc2p auxiliary factor. This stimulation is inhibited by Eco1p acetylation of Smc3p at an interface with Scc2p. It was unclear how cohesins ATPase activity is stimulated by Scc2p, or how acetylation inhibits Scc2p, given that the acetylation site is distal to cohesins ATPase active sites. Here, we identify mutations in budding yeast that suppressed the in vivo defects caused by Smc3p acetyl-mimic and acetyl-defective mutations. We provide compelling evidence that Scc2p activation of cohesin ATPase depends upon an interface between Scc2p and a region of Smc1p proximal to cohesins Smc3p ATPase active site. Furthermore, substitutions at this interface increase or decrease ATPase activity to overcome ATPase modulation by acetyl-mimic and - null mutations. Using these observations and a cryo-EM structure, we propose a model for regulating cohesin ATPase activity. We suggest that Scc2p binding to Smc1p causes a shift in adjacent Smc1p residues and ATP, stimulating the Smc3p ATPase. This stimulatory shift is inhibited through acetylation of the distal Scc2p-Smc3 interface.