Fig. 6. Condensin I is required for longitudinal chromosome compaction in prolonged prometaphase. (A) Identification of chromosome 1. Spread chromosomes were stained for heterochromatin with distamycin (DA) followed by DAPI staining. Arrows indicate chromosome 1 with characteristic pericentromeric heterochromatin. (B) Quantitative analysis of chromosome length after nocodazole treatment in cells depleted of condensin I or II. Forty-eight hours after transfection with CAP-D2 or CAP-D3 siRNAs, cells were either incubated with or without nocodazole for 4 hours before being processed for chromosome spreading and DA-DAPI staining. The telomere-to-centromere-to-telomere distance of chromosome 1 was measured in 30 cells for each experiment (exemplified by a dashed line in A), and the average length by which chromosomes shortened during the 4-hour nocodaozole treatment was calculated.