Molecular Mechanism of Condensin I Activation by KIF4A

During mitosis, the condensin I and II complexes compact chromatin into chromosomes. Loss of the chromokinesin, KIF4A, results in reduced condensin I chromosome association. However, the molecular mechanism behind this phenotype is unknown. Here, we show that KIF4A binds directly to condensin I HAWK subunit, NCAPG, via a conserved disordered short linear motif (SLiM) found in its C-terminal tail. KIF4A binding directly competes with two auto-inhibitory interactions in condensin I, mediated by SLiMs found in the N-terminus of NCAPH and the C-terminus of NCAPD2, which bind sites that overlap with KIF4A binding on NCAPG. Addition of the KIF4A SLiM peptide alone is sufficient to stimulate condensins ATPase and DNA loop extrusion activity. We also identify SLiMs in known yeast condensin interactors, Sgo and Lrs4, that bind yeast Ycg1, the HAWK equivalent to NCAPG. Our findings, together with previous work on condensin II and cohesin, demonstrate that SLiMs binding to HAWK subunits is a conserved mechanism of regulation in SMC complexes.