CDCA5 (Sororin) is essential for the establishment of sister chromatid cohesion in mammalian cells (Rankin et al. 2005) in the S-phase of the cell cycle (Nishiyama et al. 2010). Several factors contribute to the recruitment of CDCA5 to chromatin-associated cohesin: DNA replication (i.e. presence of two sister chromatids), association of cohesin complex with PDS5, and acetylation of the SMC3 cohesin subunit by ESCO1/ESCO2 acetyltransferases. Experiments in which a recombinant tagged mouse CDCA5 was expressed in human HeLa cell line showed that CDCA5 starts to accumulate on chromatin in S-phase and dissociates from chromosomal arms in prophase (Nishiyama et al. 2010). CDCA5 is essential for the establishment of chromosomal cohesion only in the presence of WAPAL, suggesting that the key role of CDCA5 (Sororin) is to antagonize WAPAL. Both CDCA5 and WAPAL contain an FGF (phenylalanine-glycine-phenylalanine) motif that is essential for PDS5 binding and is also essential for CDCA5 function in cohesion establishment. Indeed, CDCA5 is able to displace WAPAL from PDS5:WAPAL heterodimers in vitro. In vivo experiments in Xenopus egg extracts suggest that CDCA5 rearranges the topology of cohesin associated proteins so that WAPAL is no longer able to inhibit sister chromatid cohesion but remains associated with cohesin (Nishiyama et al. 2010).