In addition to extruding DNA loops, cohesin entraps within its SMC-kleisin ring (S-K) individual DNAs during G1 and sister DNAs during S-phase. All three activities require related hook-shaped proteins called Scc2 and Scc3. Using thiol-specific crosslinking we provide rigorous proof of entrapment activity in vitro. Scc2 alone promotes entrapment of DNAs in the E-S and E-K compartments, between ATP-bound engaged heads and the SMC hinge and associated kleisin, respectively. This does not require ATP hydrolysis nor is it accompanied by entrapment within S-K rings, which is a slower process requiring Scc3. Cryo-EM reveals that DNAs transported into E-S/E-K compartments are "clamped" in a sub-compartment created by Scc2's association with engaged heads whose coiled coils are folded around their elbow. We suggest that clamping may be a recurrent feature of cohesin complexes active in loop extrusion and that this conformation precedes the S-K entrapment required for sister chromatid cohesion.

中文翻译：

---

黏附蛋白内ATP依赖的DNA转运：Scc2将DNA夹在已接合的头部顶部，而Scc3促进SMC-kleisin环内的包裹

除了挤压DNA环外，粘着蛋白还可以在G1期间夹在其SMC-kleisin环（SK）内，而在S阶段则夹在其姊妹DNA内。所有这三个活动都需要相关的钩形蛋白，称为Scc2和Scc3。使用硫醇特异性交联，我们提供了体外诱捕活性的严格证据。单独的Scc2促进DNA捕获在ES和EK隔室中，分别在ATP结合的接合头与SMC铰链和相关的kleisin之间。这不需要ATP水解，也不需要伴随SK环内的截留，这是需要Scc3的较慢过程。Cryo-EM发现，转运到ES / EK隔室中的DNA被“夹紧”在由Scc2与接合的头相关的子隔间中，该结合的头的卷曲线圈围绕其肘部折叠。