RNA Processing Factors Swd2.2 and Sen1 Antagonize RNA Pol III-Dependent Transcription and the Localization of Condensin at Pol III Genes

Condensin-mediated chromosome condensation is essential for genome stability upon cell division. genetic studies have indicated that the association of condensin with chromatin is intimately linked to gene transcription,but what transcription-associated feature(s) direct(s) the accumulation of condensin remains unclear. here we show in fission yeast that condensin becomes strikingly enriched at rna pol iii-transcribed genes when swd2.2 and sen1,two factors involved in the transcription process,are simultaneously deleted. sen1 is an atp-dependent helicase whose orthologue in saccharomyces cerevisiae contributes both to terminate transcription of some rna pol ii transcripts and to antagonize the formation of dna:rna hybrids in the genome. using two independent mapping techniques,we show that dna:rna hybrids form in abundance at pol iii-transcribed genes in fission yeast but we demonstrate that they are unlikely to faciliate the recruitment of condensin. instead,we show that sen1 forms a stable and abundant complex with rna pol iii and that swd2.2 and sen1 antagonize both the interaction of rna pol iii with chromatin and rna pol iii-dependent transcription. when swd2.2 and sen1 are lacking,the increased concentration of rna pol iii and condensin at pol iii-transcribed genes is accompanied by the accumulation of topoisomerase i and ii and by local nucleosome depletion,suggesting that pol iii-transcribed genes suffer topological stress. we provide evidence that this topological stress contributes to recruit and/or stabilize condensin at pol iii-transcribed genes in the absence of swd2.2 and sen1. our data challenge the idea that a processive rna polymerase hinders the binding of condensin and suggest that transcription-associated topological stress could in some circumstances facilitate the association of condensin. © 2014 legros et al.