Directory
Condensin loop extrusion properties, roadblocks, and role in homology search during recombination in S. cerevisiae.
EMBO J, 45(9):3124-3155.
The in vivo mechanism, cis-acting roadblocks, and biological functions of DNAloop extrusion by eukaryotic SMC complexes remain incompletely defined. Here, weidentify condensin-dependent Hi-C contact stripes at the recombination enhancer(RE) and at rDNA in S. cerevisiae. The RE is an autonomous condensin loading siteonly active in MATa cells from which oriented, unidirectional loop extrusionproceeds with an estimated processivity ~150-250 kb and a density ~0.04-0.18 thatvaries across the cell cycle. Centromeres, replication forks, and highlytranscribed RNA PolII-dependent genes represent roadblocks for condensin. Cohesinis not an obstacle for condensin, while Top2 promotes its loop extrusionactivity. A DNA double-strand break (DSB) at MAT blocks loop extrusion, resultingin the establishment of a ~170 kb-long RE-MAT loop. The RE and the DSB arerequired and sufficient to form this site-specific loop, which promotesRE-proximal homology identification in the early stages of recombinational DNAbreak-repair. We propose that juxtaposition of the broken MATa site and itstarget HMLα donor is the relevant structure by which condensin promotes a-to-αmating-type switching.
Document Actions
