CDK1-mediated phosphorylation of GORASP1 (GRASP65) enables GORASP1 to recruit PLK1 (Preisinger et al. 2005). PLK1 phosphorylates GORASP1 on serine residue S189 (Sengupta and Linstedt 2010). This serine residue is near the GORASP1 region involved in GORASP1 dimerization and oligomerization, a process underlying the stacking of cis-Golgi cisternae (Wang et al. 2003). The phosphorylation of S189 by PLK1 impairs Golgi cisternae stacking (tethering), contributing to Golgi unlinking and fragmentation in mitosis, probably by preventing formation of GORASP1 dimers and oligomers (Sutterlin et al. 2001, Sengupta and Linstedt, 2010). Two other potential phosphorylation sites that match PLK1 substrate consensus sequence exist in GORASP1, but their functional significance has not yet been examined (Sengupta and Linstedt, 2010).