Figure 1. Possible mechanisms of cohesion establishment.

(A) Cohesin complexes previously associated with un-replicated DNA converted into cohesive ones behind the replication fork (Cohesin conversion) or cohesion built by de novo loading of cohesin molecules onto nascent DNAs at the replication forks (de novo loading).(B) The replisome-associated proteins that affect cohesion establishment belong to two epistasis groups, one containing Chl1, Ctf4, Csm3 and Tof1 and a second containing Mrc1 as well as the Ctf18-RFC. Combining two mutants from the same group has little or no additional effect on viability and causes no greater cohesion defect than the single mutants, while combining mutants from different groups either causes lethality or synthetic sickness and, when measured using conditional alleles, greatly increased defects in sister chromatid cohesion. Data from Xu et al., 2007. (C) The approximate positions of the Tof1/Csm3, Ctf4, Chl1, Mrc1 and the Ctf18-RFC within the replisome is shown (Baretić et al., 2020; Grabarczyk et al., 2018; Simon et al., 2014; Villa et al., 2016).