Abstract
The mechanisms leading to the accumulation of the SMC complexes condensins around specific transcription units remain unclear. Observations made in bacteria suggested that RNA polymerases (RNAPs) constitute an obstacle to SMC translocation, particularly when RNAP and SMC travel in opposite directions. Here we show in fission yeast that gene termini harbour intrinsic condensin-accumulating features whatever the orientation of transcription, which we attribute to the frequent backtracking of RNAP at gene ends. Consistent with this, to relocate backtracked RNAP2 from gene termini to gene bodies was sufficient to cancel the accumulation of condensin at gene ends and to redistribute it evenly within transcription units, indicating that RNAP backtracking may play a key role in positioning condensin. Formalization of this hypothesis in a mathematical model suggests that the inclusion of a sub-population of RNAP with longer dwell-times is essential to fully recapitulate the distribution profiles of condensin around active genes. Taken together, our data strengthen the idea that dense arrays of proteins tightly bound to DNA alter the distribution of condensin on chromosomes.
Highlights
Structural maintenance of chromosomes (SMC) complexes are essential for the organization and stability of chromosomes from bacteria to humans (Uhlmann, 2016; Hassler et al, 2018; van Ruiten & Rowland, 2018)
We have previously proposed that fission yeast condensin might load onto DNA at nucleosome-depleted promoters of active genes (Toselli-Mollereau et al, 2016) and would subsequently accumulate towards the 39 of genes actively transcribed by RNAP2 (Sutani et al, 2015; Toselli-Mollereau et al, 2016)
We showed that to interfere with RNAP3 transcription termination alters the distribution of condensin, suggesting that transcription termination defects impact the accumulation of condensin, whatever the RNA polymerases (RNAPs) involved
Summary
Structural maintenance of chromosomes (SMC) complexes are essential for the organization and stability of chromosomes from bacteria to humans (Uhlmann, 2016; Hassler et al, 2018; van Ruiten & Rowland, 2018). It was proposed that condensin is actively recruited at transcription termination regions because they accumulate single-stranded DNA and/or chromatinassociated RNA molecules that interfere with the organization of mitotic chromosomes (Sutani et al, 2015; Nakazawa et al, 2019a).
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