Fig. 6.

Summary of results and DPY-21 function in condensin DC-mediated X chromosome repression. In a wild-type hermaphrodite cell, condensin DC binds dynamically and specifically to the X chromosomes. This binding is disrupted by knockdown of the condensing DC recruiter SDC-2 or a single amino acid mutation in the ATPase domain of DPY-27. Condensin DC may interact with histone tails through HEAT repeats within DPY-28. The H4K20me2 demethylase DPY-21 has a dual function in X chromosome repression. The catalytic activity reduces H4K20me2 and H4K20me3 and increases H4K20me1 on the X chromosome. This leads to reduced H4K16ac and contributes to repression. The non-catalytic activity of DPY-21 increases the mobility of condensin DC molecules, which is important for transcription repression. In the dpy-21 null condition, both catalytic and non-catalytic activities are eliminated, resulting in stronger X chromosome derepression.