The cis element and factors required for condensin recruitment to chromosomes.

Condensins are required for segregation of rDNA repeats in concert with Fob1, a replication fork block protein binding at the replication fork barrier (RFB) site within rDNA in yeast. Here, we found that the RFB site functions as a cis element for Fob1-dependent condensin recruitment onto chromosomes. Replication fork blockage itself is not necessary for condensin recruitment. Instead, by genetic screening, we identified three genes, TOF2, CSM1, and LRS4, required both for condensin recruitment to the RFB site and for assuring the segregation of rDNA repeats. Hierarchical binding of Fob1, these three proteins and condensin, and interactions between Csm1/Lrs4 and multiple subunits of condensin were observed. These results suggest that three proteins control protein interactions linking between Fob1 and condensin, and contribute to ensuring the faithful segregation of rDNA repeats. Our study also suggests that recruitment of condensin onto chromosomes requires cis elements and recruiters that physically interact with condensin.