RNA Pol II transcription antagonises mitotic chromosome assembly and segregation by condensin

Condensin drives mitotic chromosome assembly by folding chromatin into loops and is enriched in the vicinity of highly expressed genes, but the significance of such proximity with respect to condensin activity has remained unclear. Here, by modulating the occupancy of RNA Pol II in vivo, we show that transcription plays no role in the steady state association of condensin with DNA. Rather, transcription stalls and even displaces condensin, hindering its ability to fold chromatin and to support chromosome segregation. Our results highlight a key aspect of the integrated functioning of condensin and suggest that a tight control of transcription underlies mitotic chromosome assembly. Overall design: calibrated chromatin immunoprecipitation (calChIPseq) experiment against GFP-tagged kleisin Cnd2 (A111-22 antibody) from the condensin SMC complex and Hi-C experiments in Dhp1-3xsAID (XRN2 5\222xoribonuclease) and Rpb1-3xsAID (RPB1 large subunit of RNAPII) degron tagged strains treated with or without auxin. calibrated chromatin immunoprecipitation was performed against Rpb1 (8WG16 antibody) as control in Rpb1-3xsAID strains. Calibrated chromatin immunoprecipitation (calChIPseq) experiment against Rpb1 using 8WG16 antibody in Dhp1-3xsAID cells treated with NaOH or 5-adamantyl-IAA and Hi-C experiments in wild-type and Cut14-3xsAID cells treated with 5-adamantyl-IAA.