Sister chromatid cohesion halts DNA loop expansion.

Eukaryotic genomes are folded into DNA loops mediated by structural maintenance of chromosomes (SMC) complexes such as cohesin, condensin, and Smc5/6. This organization regulates different DNA-related processes along the cell cycle, such as transcription, recombination, segregation, and DNA repair. During the G2 stage, SMC-mediated DNA loops coexist with cohesin complexes involved in sister chromatid cohesion (SCC). However, the articulation between the establishment of SCC and the formation of SMC-mediated DNA loops along the chromatin remains unknown. Here, we show that SCC is indeed a barrier to cohesin-mediated DNA loop expansion along G2/M Saccharomyces cerevisiae chromosomes.