Condensin IDC has a Functional ATPase That is Required for X-Chromosome Dosage Compensation in <i>C. elegans</i>

Dosage compensation (DC) in C. elegans utilizes a condensin complex that resembles mitotic condensins, but differs by one subunit, DPY-27. DPY-27 replaces SMC-4, one of the Structural Maintenance of Chromosome (SMC) proteins that is responsible for hydrolyzing ATP, required for condensation of DNA and other mitotic condensin functions. To understand if the ATPase function is required in DC, we first demonstrated that DPY-27 is capable of hydrolyzing ATP in vitro. Then, we used CRISPR/Cas9-mediated genome editing to generate an ATPase mutation in dpy-27. Although the mutant protein is expressed and it is incorporated into the condensin IDC complex, this mutation results in a loss of DC. Specifically, we found that without ATPase function, DPY-27 containing condensin IDC has reduced capacity to bind DNA, condense the X chromosomes, and facilitate H4K20me1 enrichment on the X-chromosomes. Our results suggest that condensin IDC, like mitotic condensins, uses ATP hydrolysis to perform its functions, making C. elegans DC a model for how activities attributed to mitotic condensins can be used to regulate gene expression.