2 1 ▁bind s ▁on ▁both ▁S MC 1 ▁and ▁S MC 3 , ▁the ▁coh es in ▁complex ▁forms ▁a ▁closed ▁ring ▁structure . ▁The ▁interfaces ▁between ▁the ▁S MC ▁sub un its ▁and ▁R AD 2 1 ▁can ▁open ▁to ▁allow ▁DNA ▁to ▁pass ▁in ▁and ▁out ▁of ▁the ▁coh es in ▁ring . ▁ ▁While ▁structures ▁are ▁available ▁for ▁many ▁of ▁the ▁sub un its ▁and ▁their ▁interfaces , ▁a ▁structure ▁of ▁the ▁entire ▁coh es in ▁complex ▁has ▁not ▁been ▁solved . ▁Our ▁knowledge ▁of ▁the ▁con formation ▁of ▁the ▁coh es in ▁comes ▁largely ▁from ▁electron ▁micro sc opy . ▁These ▁studies ▁have ▁revealed ▁coh es in ▁in ▁numerous ▁conform ations ▁including ▁rings , ▁el ong ated ▁ro ds ▁and ▁most ▁recently ▁in ▁a ▁fol ded ▁conform ations . ▁It ▁is ▁not ▁known ▁which ▁con formation ▁is ▁pre domin ant ▁inside ▁the ▁cell ▁and ▁whether ▁some ▁are ▁induced ▁by ▁sample ▁prepar ation . ▁ ▁Function ▁ ▁The ▁coh es in ▁ring ▁has ▁many ▁functions : ▁▁ 1 . ▁It ▁is ▁used ▁to ▁keep ▁the ▁sister ▁chrom at ids ▁connected ▁with ▁each ▁other ▁during ▁met aph ase ▁ens uring ▁that ▁during ▁mit osis ▁( and ▁me ios is ), ▁each ▁sister ▁chrom at id ▁seg reg ates ▁to ▁opposite ▁pol es . ▁Without ▁coh es in , ▁the ▁cell ▁would ▁be ▁unable ▁to ▁control ▁sister ▁chrom at id ▁seg reg ation ▁since ▁there ▁would ▁be ▁no ▁way ▁of ▁ens uring ▁whether ▁the ▁sp ind le ▁fi ber ▁attached ▁on