fig4: 4C reveals interactions between pericentromeres of different chromosomes. (A) Primers were used to assay interactions, via 3C technique, between the pericentromeres and arms of chromosome III and V (see Materials and methods). The interaction index is the ratio of the pericentromere (P) to the arm (A; control for random interactions) PCR product was normalized to 1. Pericentromere interaction index is shown for WT, cin8Δ, brn1-9, mcm21Δ, and GalCEN3 (conditionally off centromere). Values listed in Table 1. Error bars represent standard deviations. Asterisks denote significant difference from WT (P < 0.01). Mutants with a different number of asterisks are significantly different, whereas those with the same numbers are similar. (B) Diagram depicting the half-spindle and a results summary for WT and mutants. kMTs emanate from the spindle pole each bound to a different chromosome at the kinetochore/centromere, whereas interpericentromere interaction is facilitated by a cross-linker. Results of 4C suggest cohesin and condensin act as a cross-linker between different pericentromeres. Plus signs, statistically similar to WT; minus, decreased significantly relative to WT; double minus, decreased significantly relative to single minus; N/A, not applicable.

Mentions: To determine whether pericentromeres are in physical proximity in metaphase, we adapted the 3C (chromosome conformation capture) technique to probe the interaction between two loci on different chromosomes. Inverse primer pairs were used to map the interaction of chromosome 3 and 5 at arm and pericentromere loci (see Materials and methods). Arm loci were used as a control for random interactions between chromosomes 3 and 5. We found that WT pericentromeres interact 1.75 ± 0.05–fold more than random arm interaction (pericentromere/arm, normalized to arm 1.00, n = 10; Fig. 4 A). This recapitulates initial findings of interpericentromere interactions via 3C techniques (cross-linking frequency 1.5; Dekker et al., 2002).