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. 2012 Mar 15;125(6):1591–1604. doi: 10.1242/jcs.097790

Fig. 9.

Fig. 9.

A model displaying the contrasting roles of condensin I and II. Based on proteomics data showing a 10:1 ratio of condensin I to condensin II on mitotic chromosomes (Ohta et al., 2010) and our own results, we propose the following unifying model for condensin I and II function in mitotic chromosomes. The size of condensin I and II reflects the known size relative to DNA based on atomic force measurements (Anderson et al., 2002; Yoshimura et al., 2002). Top panel: individual rosette layers showing localisation of condensin I and II. Bottom: rosette layers stacked together showing the effect on longitudinal axial compaction in the presence and absence of condensins. We propose that, in wild-type mitotic chromosomes, condensin I stabilises and nucleates short-range loops, promoting compaction of chromosome rosettes. Condensin II provides the long-range linkage and alignment between the rosettes, thus facilitating chromosome longitudinal compaction. Chromosomes deficient of condensin I (Δ condensin I) are unable to link and nucleate short-range loops, resulting in a fatter and disorganized chromosome scaffold. Chromosomes deficient of condensin II (Δ condensin II) are unable to provide regular structural linkage between rosettes. Discrete rosettes are unable to form, resulting in a thinner chromosome lacking structural integrity.