Link to bioRxiv paper: http://biorxiv.org/cgi/content/short/2020.11.04.368506v1?rss=1 Authors: Ryu, J.-K., Rah, S.-H., Janissen, R., Kerssemakers, J. W. J., Dekker, C. Abstract: The condensin SMC protein complex organizes chromosomal structure by extruding loops of DNA. Its ATP-dependent motor mechanism remains unclear but likely involves steps associated with large conformational changes within the ~50 nm protein complex. Here, using magnetic tweezers, we resolve single steps in loop extrusion by individual yeast condensins. Step sizes range between 20-45 nm at forces of 1.0-0.2 pN, respectively, comparable to the complex size. The large steps show that condensin reels in DNA in very sizeable amounts, up to ~600 bp per extrusion step, consistent with the non-stretched DNA polymer at these low forces. Using ATP-binding-impaired and ATP-hydrolysis-deficient mutants, we find that ATP binding is the primary step-generating stage underlying DNA loop extrusion. We discuss the findings in terms of a scrunching model where a stepwise DNA loop extrusion is generated by an ATP-binding-induced engagement of the hinge and the globular domain of the SMC complex. Copy rights belong to original authors. Visit the link for more info