Biology subjects

Shaltiel, I. A.

Publications and source records attributed to Shaltiel, I. A..

3 recordsLinked to original sources

bioRxiv2021

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

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.

biochemistry↗

bioRxiv2019

DNA-loop extruding condensin complexes can traverse one another

Condensin, a key member of the Structure Maintenance of Chromosome (SMC) protein complexes, has recently been shown to be a motor that extrudes loops of DNA1. It remains unclear, however, how condensin complexes work together to collectively package DNA into the chromosomal architecture. Here, we use time-lapse single-molecule visualization to study mutual interactions between two DNA-loop-extruding yeast condensins. We find that these one-side-pulling motor proteins are able to dynamically change each others DNA loop sizes, even when located large distances apart. When coming into close proximity upon forming a loop within a loop, condensin complexes are, surprisingly, able to traverse each other and form a new type of loop structure, which we term Z loop - three double-stranded DNA helices aligned in parallel with one condensin at each edge. These Z-loops can fill gaps left by single loops and can form symmetric dimer motors that reel in DNA from both sides. These new findings indicate that condensin may achieve chromosomal compaction using a variety of looping structures.

biophysics↗

bioRxiv2018

Condensin II inactivation in interphase does not affect chromatin folding or gene expression

Condensin complexes have been proposed to play a prominent role in interphase chromatin organization and control of gene expression. Here, we report that the deletion of the central condensin II kleisin subunit Ncaph2 in differentiated mouse hepatocytes does not lead to significant changes in chromosome organization or in gene expression. Both observations challenge current views that implicate condensin in interphase chromosomal domain formation and in enhancer-promoter interactions. Instead, we suggest that the previously reported effects of condensin perturbation may result from their structural role during mitosis, which might indirectly impact the re-establishment of interphase chromosomal architecture after cell division.

genomics↗