Project description:The type II topoisomerases, gyrase and topoisomerase IV, are essential enzymes in nearly all bacteria and are the targets of fluoroquinolones, which are some of the most widely prescribed broad-spectrum antibacterials in clinical use. As part of their catalytic cycle, gyrase and topoisomerase IV transiently cleave DNA in a sequence-dependent manner. However, it is unclear whether this sequence-dependence is species-specific. Therefore, using our recently developed SHAN-seq method, we mapped and compared cleavage sites for type II topoisomerases from three different pathogenic bacterial species, Escherichia coli, Bacillus anthracis, and Mycobacterium tuberculosis in the presence of the fluoroquinolone, ciprofloxacin. We found that the enzymes have substantially different DNA cleavage specificities that vary between gyrase and topoisomerase IV, across species, with supercoil chirality, and in response to ciprofloxacin. Our results demonstrate that bacterial species fine-tune the DNA cleavage specificity of their type II topoisomerases. This finding suggests that cleavage specificity may play important physiological roles and, in turn, may affect the susceptibility of bacteria to fluoroquinolone antibacterials.
Project description:Here we dissect the transcriptional response in S. cerevisiae cells lacking DNA topoisomerases. We use microarray technology coupled with a functional genomics approach and demonstrate intimate connections between topoisomerase dependency, promoter chromatin architecture and gene transcription. Our findings suggest that DNA topoisomerases I and II play a role for transcription initiation. We observe a genome wide reduction in mRNA levels and identify a distinct functional subset of the genome with particular requirements for topoisomerases. These genes are characterized by high transcriptional plasticity, they are chromatin regulated and distinguished by having an enrichment of a nucleosome at a critical position in the promoter region, suggesting that topoisomerases influence transcription initiation by affecting promoter chromatin structure. In further support of a role of topoisomerases for initiation, we demonstrate that genome wide topoisomerase dependency reflects transcriptional activity but not transcriptional length. We exemplify the importance of topoisomerases for initiation of chromatin-regulated genes by showing that the enzymes are essential although redundant for PHO5 induction and are necessary for a step required for promoter nucleosome removal. W303 versus top1Î?, top2ts and top1Î?top2ts. 3 biological replicates for each mutant versus wildtype counterpart amounting to 12 microarrays.
Project description:To investigate the role of DNA topoisomerases in transcription, we have studied global gene expression in Saccharomyces cerevisiae cells deficient for topoisomerases I and II and performed single-gene analyses to support our findings. The genome-wide studies show a general transcriptional down-regulation upon lack of the enzymes, which correlates with gene activity but not gene length. Furthermore, our data reveal a distinct subclass of genes with a strong requirement for topoisomerases. These genes are characterized by high transcriptional plasticity, chromatin regulation, TATA box presence, and enrichment of a nucleosome at a critical position in the promoter region, in line with a repressible/inducible mode of regulation. Single-gene studies with a range of genes belonging to this group demonstrate that topoisomerases play an important role during activation of these genes. Subsequent in-depth analysis of the inducible PHO5 gene reveals that topoisomerases are essential for binding of the Pho4p transcription factor to the PHO5 promoter, which is required for promoter nucleosome removal during activation. In contrast, topoisomerases are dispensable for constitutive transcription initiation and elongation of PHO5, as well as the nuclear entrance of Pho4p. Finally, we provide evidence that topoisomerases are required to maintain the PHO5 promoter in a superhelical state, which is competent for proper activation. In conclusion, our results reveal a hitherto unknown function of topoisomerases during transcriptional activation of genes with a repressible/inducible mode of regulation
Project description:When DNA is unwound during replication, it becomes overtwisted and forms positive supercoils in front of the translocating DNA polymerase. Unless removed or dissipated, this superhelical tension can impede replication elongation. Topoisomerases, including gyrase and topoisomerase IV in bacteria, are required to relax positive supercoils ahead of DNA polymerase, but may not be sufficient for replication. Here, we find that GapR, a chromosome structuring protein in Caulobacter crescentus, is required to complete DNA replication. GapR associates in vivo with positively supercoiled chromosomal DNA, and our biochemical and structural studies demonstrate that GapR forms a dimer-of-dimers that fully encircles overtwisted DNA. Further, we show that GapR stimulates gyrase and topo IV to relax positive supercoils, thereby enabling DNA replication. Analogous chromosome structuring proteins that locate to the overtwisted DNA in front of replication forks may be present in other organisms, similarly helping to recruit and stimulate topoisomerases during DNA replication.
Project description:Condensin complexes are evolutionarily conserved molecular motors from the structural maintenance of chromosomes (SMC) family, that use ATPase activity to translocate along DNA and form loops. Condensin and topoisomerase II (TOP-2) are essential for the structure and function of mitotic chromosomes. While condensin-mediated DNA looping is thought to direct TOP-2 chain-passing activity to separate sister chromatids, it is not known if TOP-2 in turn regulates loop formation. Here we used an X chromosome specific condensin that represses transcription for dosage compensation in C.elegans, to determine how DNA topology affects SMC translocation in vivo. We applied auxin-inducible degradation of topoisomerases I and II to determine their effect on condensin DC binding and function. We found that both topoisomerases colocalize with condensin DC and control its movement at different genomic scales. TOP-2 depletion hindered condensin DC spreading over long distances, resulting in accumulation around its X-specific recruitment sites and shorter Hi-C interactions. In contrast, TOP-1 depletion did not affect long-range spreading but resulted in accumulation of condensin DC within gene bodies, specially of highly expressed and long genes. Both TOP-1 and TOP-2 depletion resulted in X chromosome upregulation indicating that condensin DC translocation at both scales is required for its function in transcriptional repression. Together our work reveals distinct DNA topological requirements for two modes of condensin DC association with chromatin: long-range linear translocation that requires decatenation and unknotting of DNA and short-range binding to genes that requires resolution of transcription-induced supercoiling.
Project description:Condensin complexes are evolutionarily conserved molecular motors from the structural maintenance of chromosomes (SMC) family, that use ATPase activity to translocate along DNA and form loops. Condensin and topoisomerase II (TOP-2) are essential for the structure and function of mitotic chromosomes. While condensin-mediated DNA looping is thought to direct TOP-2 chain-passing activity to separate sister chromatids, it is not known if TOP-2 in turn regulates loop formation. Here we used an X chromosome specific condensin that represses transcription for dosage compensation in C.elegans, to determine how DNA topology affects SMC translocation in vivo. We applied auxin-inducible degradation of topoisomerases I and II to determine their effect on condensin DC binding and function. We found that both topoisomerases colocalize with condensin DC and control its movement at different genomic scales. TOP-2 depletion hindered condensin DC spreading over long distances, resulting in accumulation around its X-specific recruitment sites and shorter Hi-C interactions. In contrast, TOP-1 depletion did not affect long-range spreading but resulted in accumulation of condensin DC within gene bodies, specially of highly expressed and long genes. Both TOP-1 and TOP-2 depletion resulted in X chromosome upregulation indicating that condensin DC translocation at both scales is required for its function in transcriptional repression. Together our work reveals distinct DNA topological requirements for two modes of condensin DC association with chromatin: long-range linear translocation that requires decatenation and unknotting of DNA and short-range binding to genes that requires resolution of transcription-induced supercoiling.
Project description:During meiotic prophase, concurrent transcription, recombination, and chromosome synapsis place substantial topological strain on chromosomal DNA, but the role of topoisomerases in this context remains poorly defined. Here, we analyzed the roles topoisomerases I and II (Top1 and Top2) during meiotic prophase in Saccharomyces cerevisiae. We show that both topoisomerases accumulate primarily in promoter-containing intergenic regions of actively transcribing genes, including many meiotic double-strand break (DSB) hotspots. Despite the comparable binding patterns, top1 and top2 mutations have different effects on meiotic recombination. TOP1 disruption delays DSB induction and shortens the window of DSB accumulation by an unknown mechanism. By contrast, temperature-sensitive top2-1 mutants exhibit a marked delay in meiotic chromosome remodeling and elevated DSB signals on synapsed chromosomes. The problems in chromosome remodeling were linked to altered Top2 binding patterns rather than a loss of Top2 catalytic activity and stemmed from a defect in recruiting the chromosome remodeler Pch2/TRIP13 to synapsed chromosomes. No chromosomal defects were observed in the absence of TOP1. Our results imply independent roles for topoisomerases I and II in modulating meiotic chromosome structure and recombination.
Project description:Condensin complexes are evolutionarily conserved molecular motors from the structural maintenance of chromosomes (SMC) family, that use ATPase activity to translocate along DNA and form loops. Condensin and topoisomerase II (TOP-2) are essential for the structure and function of mitotic chromosomes. While condensin-mediated DNA looping is thought to direct TOP-2 chain-passing activity to separate sister chromatids, it is not known if TOP-2 in turn regulates loop formation. Here we used an X chromosome specific condensin that represses transcription for dosage compensation in C.elegans, to determine how DNA topology affects SMC translocation in vivo. We applied auxin-inducible degradation of topoisomerases I and II to determine their effect on condensin DC binding and function. We found that both topoisomerases colocalize with condensin DC and control its movement at different genomic scales. TOP-2 depletion hindered condensin DC spreading over long distances, resulting in accumulation around its X-specific recruitment sites and shorter Hi-C interactions. In contrast, TOP-1 depletion did not affect long-range spreading but resulted in accumulation of condensin DC within gene bodies, specially of highly expressed and long genes. Both TOP-1 and TOP-2 depletion resulted in X chromosome upregulation indicating that condensin DC translocation at both scales is required for its function in transcriptional repression. Together our work reveals distinct DNA topological requirements for two modes of condensin DC association with chromatin: long-range linear translocation that requires decatenation and unknotting of DNA and short-range binding to genes that requires resolution of transcription-induced supercoiling.