▁dim er ▁where ▁each ▁ring ▁surr ounds ▁one ▁sister ▁chrom at id . ▁The ▁two ▁rings ▁are ▁connected ▁to ▁each ▁other ▁through ▁formation ▁of ▁a ▁bridge ▁that ▁holds ▁the ▁two ▁sister ▁chrom at ids ▁together . ▁ ▁The ▁topology ▁and ▁structure ▁of ▁these ▁sub un its ▁has ▁been ▁best ▁character ized ▁in ▁bud ding ▁ye ast , ▁but ▁the ▁sequence ▁conservation ▁of ▁these ▁prote ins ▁and ▁bio chem ical ▁and ▁electron ▁micro scop ic ▁observations ▁imply ▁that ▁coh es in ▁complex es ▁in ▁other ▁species ▁are ▁very ▁similar ▁in ▁their ▁structure , ▁. ▁▁ ▁The ▁coh es in ▁complex ▁is ▁established ▁during ▁the ▁initial ▁stages ▁of ▁S - phase . ▁The ▁complex es ▁associate ▁with ▁chrom os om es ▁before ▁DNA ▁rep lication ▁occurs . ▁Once ▁cells ▁start ▁rep lic ating ▁their ▁DNA , ▁coh es in ▁rings ▁close ▁and ▁link ▁the ▁sister ▁chrom at ids ▁together . ▁C oh es in ▁complex es ▁must ▁be ▁present ▁during ▁S - phase ▁in ▁order ▁for ▁coh es ion ▁to ▁take ▁place . ▁It ▁is ▁unclear , ▁however , ▁how ▁coh es in ▁is ▁loaded ▁on ▁the ▁chrom os om es ▁during ▁G 1 . ▁There ▁are ▁two ▁proposed ▁hypoth eses ▁so ▁far : ▁▁ ▁The ▁ATP ase ▁domain ▁of ▁the ▁S MC ▁prote ins ▁interact s ▁with ▁DNA ▁and ▁this ▁interaction ▁initially ▁medi ates ▁the ▁loading ▁of ▁coh es in ▁complex es ▁on ▁chrom os om es . ▁ ▁Several ▁prote ins ▁aid ▁in ▁the ▁loading ▁process . ▁For ▁example , ▁S cc 2