Cdk1 (Cdc2) in complex with Ccnb (cyclin B) phosphorylates condensin I subunits Ncapd2, Ncapg and Ncaph in mitotic Xenopus egg extracts. While phosphorylation sites in Ncapg and Ncaph have not been identified, Ncapd2 is phosphorylated on threonine residues T1314, T1348 and T1353 (Kimura et al. 1998) which are conserved in human and mouse orthologs. Phosphorylation by Cdk1 enables condensin I to introduce positive supercoils into DNA and promotes chromatin condensation (Kimura et al. 1998).