Protein levels of condensin subunits are constant during the cell cycle. Four subunits, SMC4, NCAPD2, NCAPG and NCAPH, are phosphorylated in interphase cells (Takemoto et al. 2004) by CK2 i.e. casein kinase II (Takemoto et al. 2006). Except for the phosphorylation of NCAPH subunit on serine residue S570, CK2 phosphorylation sites in condensin I subunits have not been identified. Phosphorylation by CK2 inhibits condensin I-mediated introduction of positive supercoils into DNA and chromatin condensation. Mitotic activation of condensin I involves removal of phosphate groups added by CK2 (Takemoto et al. 2006), but the responsible phosphatase has not been identified.