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Osmotic disruption of chromatin induces Topoisomerase 2 activity at sites of transcriptional stress [Mnase-Seq]

ABSTRACT: Transcription generates superhelical stress in DNA that poses problems for genome stability, but determining when and where such stress arises within chromosomes is challenging. Here, using G1-arrested S. cerevisiae cells, and employing rapid fixation and ultra-sensitive enrichment, we utilise the physiological activity of endogenous topoisomerase 2 (Top2) as a probe of transcription-induced superhelicity. We demonstrate that Top2 activity is surprisingly uncorrelated with transcriptional activity, suggesting that superhelical stress is obscured from Top2 within chromatin in vivo. We test this idea using osmotic perturbation—a treatment that transiently destabilises chromatin in vivo—revealing that Top2 activity redistributes within sub-minute timescales into broad zones patterned by long genes, convergent gene arrays, and transposon elements—and also by acute transcriptional induction. We propose that latent superhelical stress is normally absorbed by the intrinsic topological buffering capacity of chromatin, helping to avoid spurious topoisomerase activity arising within the essential coding regions of the genome.

ORGANISM(S): Saccharomyces cerevisiae

PROVIDER: GSE280155 | GEO | 2024/12/01

REPOSITORIES: GEO

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Project description:During chromosome duplication the parental DNA molecule becomes over-wound, or positively supercoiled, in the region ahead of the advancing replication fork. To allow fork progression this superhelical tension has to be removed by topoisomerases, which operate by introducing transient DNA breaks. Positive supercoiling can also be diminished if the advancing fork rotates along the DNA helix, but then sister chromatid intertwinings form in its wake. Despite these insights it remains largely unknown how replicationinduced superhelical stress is dealt with on linear, eukaryotic chromosomes. Here we show that this stress increases with the length of budding yeast chromosomes. This opens for the possibility that superhelical tension is handled on a chromosome scale and not only within topologically closed chromosomal domains as the current view predicts. We found that inhibition of type I topoisomerases leads to a late replication delay of longer, but not shorter chromosomes. This phenotype is also displayed by cells expressing mutated versions of the cohesin- and condensin–related Smc5/6 complex. The chromosomal association of the Smc5/6 complex is shown to increase in response to chromosome lengthening, chromosome circularization, or inactivation of Topoisomerase 2, all having the potential to increase the number of sister chromatid intertwinings 3. Furthermore, non-functional Smc6 reduces the accumulation of intertwined sister plasmids after one round of replication in the absence of Topoisomerase 2 function. Our results demonstrate that the length of a chromosome influences the need of superhelical tension release in Saccharomyces cerevisiae, and allow us to propose a model where the Smc5/6 complex facilitates fork rotation by sequestering nascent chromatid intertwinings which form behind the replication machinery. Smc6、Nse4, and Scc2 profiles with or without topological tension was analyzed (in top2 mutant, cells with circular chromosome, and fragmented chromosome) . 17 ChIP samples and corresponding WCE fractions have been analyzed.