scholarly journals Real-time imaging of DNA loop extrusion by condensin

Science ◽  
2018 ◽  
Vol 360 (6384) ◽  
pp. 102-105 ◽  
Author(s):  
Mahipal Ganji ◽  
Indra A. Shaltiel ◽  
Shveta Bisht ◽  
Eugene Kim ◽  
Ana Kalichava ◽  
...  
Keyword(s):  
Real Time ◽  
Adenosine Triphosphate ◽  
Genome Organization ◽  
Protein Complexes ◽  
Dna Loops ◽  
Base Pairs ◽  
Real Time Imaging ◽  
Condensin Complex ◽  
Dna Loop

It has been hypothesized that SMC protein complexes such as condensin and cohesin spatially organize chromosomes by extruding DNA into large loops. We directly visualized the formation and processive extension of DNA loops by yeast condensin in real time. Our findings constitute unambiguous evidence for loop extrusion. We observed that a single condensin complex is able to extrude tens of kilobase pairs of DNA at a force-dependent speed of up to 1500 base pairs per second, using the energy of adenosine triphosphate hydrolysis. Condensin-induced loop extrusion was strictly asymmetric, which demonstrates that condensin anchors onto DNA and reels it in from only one side. Active DNA loop extrusion by SMC complexes may provide the universal unifying principle for genome organization.

scholarly journals A hold-and-feed mechanism drives directional DNA loop extrusion by condensin

2021 ◽  
Author(s):  
Indra A Shaltiel ◽  
Sumanjit Datta ◽  
Léa Lecomte ◽  
Markus Hassler ◽  
Marc Kschonsak ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Single Molecule ◽  
Protein Complexes ◽  
Double Helix ◽  
Power Stroke ◽  
Reaction Cycle ◽  
Cryo Electron Microscopy ◽  
Condensin Complex ◽  
Dna Loop ◽  
Dna Double Helix

SMC protein complexes structure genomes by extruding DNA loops, but the molecular mechanism that underlies their activity has remained unknown. We show that the active condensin complex entraps the bases of a DNA loop in two separate chambers. Single-molecule and cryo-electron microscopy provide evidence for a power-stroke movement at the first chamber that feeds DNA into the SMC-kleisin ring upon ATP binding, while the second chamber holds on upstream of the same DNA double helix. Unlocking the strict separation of 'motor' and 'anchor' chambers turns condensin from a one-sided into a bidirectional DNA loop extruder. We conclude that the orientation of two topologically bound DNA segments during the course of the SMC reaction cycle determines the directionality of DNA loop extrusion.

scholarly journals AFM images of open and collapsed states of yeast condensin suggest a scrunching model for DNA loop extrusion

2019 ◽  
Author(s):  
Je-Kyung Ryu ◽  
Allard J. Katan ◽  
Eli O. van der Sluis ◽  
Thomas Wisse ◽  
Ralph de Groot ◽  
...  
Keyword(s):  
Protein Complexes ◽  
Molecular Motor ◽  
Neck Size ◽  
Force Microscopy ◽  
Double Stranded Dna ◽  
Atomic Force ◽  
Condensin Complex ◽  
Dna Loop ◽  
Structural Maintenance Of Chromosome ◽  
Collapsed States

SUMMARYStructural Maintenance of Chromosome (SMC) protein complexes are the key organizers of the spatiotemporal structure of chromosomes. The condensin SMC complex, which compacts DNA during mitosis, was recently shown to be a molecular motor that extrudes large loops of DNA. The mechanism of this unique motor, which takes large steps along DNA at low ATP consumption, remains elusive however. Here, we use Atomic Force Microscopy (AFM) to visualize the structure of yeast condensin and condensin-DNA complexes. Condensin is found to exhibit mainly open ‘O’ shapes and collapsed ‘B’ shapes, and it cycles dynamically between these two states over time. Condensin binds double-stranded DNA via a HEAT subunit and, surprisingly, also via the hinge domain. On extruded DNA loops, we observe a single condensin complex at the loop stem, where the neck size of the DNA loop correlates with the width of the condensin complex. Our results suggest that condensin extrudes DNA by a fast cyclic switching of its conformation between O and B shapes, consistent with a scrunching model.

scholarly journals Bridging-induced phase separation induced by cohesin SMC protein complexes

2021 ◽  
Vol 7 (7) ◽  
pp. eabe5905
Author(s):  
Je-Kyung Ryu ◽  
Céline Bouchoux ◽  
Hon Wing Liu ◽  
Eugene Kim ◽  
Masashi Minamino ◽  
...  
Keyword(s):  
Phase Separation ◽  
Genome Organization ◽  
Fluorescence Recovery After Photobleaching ◽  
Protein Complexes ◽  
Yeast Cells ◽  
Base Pairs ◽  
Fundamental Building Block ◽  
Structural Maintenance Of Chromosome

Structural maintenance of chromosome (SMC) protein complexes are able to extrude DNA loops. While loop extrusion constitutes a fundamental building block of chromosomes, other factors may be equally important. Here, we show that yeast cohesin exhibits pronounced clustering on DNA, with all the hallmarks of biomolecular condensation. DNA-cohesin clusters exhibit liquid-like behavior, showing fusion of clusters, rapid fluorescence recovery after photobleaching and exchange of cohesin with the environment. Strikingly, the in vitro clustering is DNA length dependent, as cohesin forms clusters only on DNA exceeding 3 kilo–base pairs. We discuss how bridging-induced phase separation, a previously unobserved type of biological condensation, can explain the DNA-cohesin clustering through DNA-cohesin-DNA bridges. We confirm that, in yeast cells in vivo, a fraction of cohesin associates with chromatin in a manner consistent with bridging-induced phase separation. Biomolecular condensation by SMC proteins constitutes a new basic principle by which SMC complexes direct genome organization.

Sign in / Sign up

Export Citation Format

Share Document