Cks85A and Skp2 interact to maintain diploidy and promote growth in Drosophila

► Drosophila Cks85A and Skp2 have dual roles in preventing and promoting polyploidy. ► Cks85A and closely related Cks30A are functionally distinct. ► Cks85A but not Cks30A, associates with SCF-Skp2. ► Cks85A functions largely or solely as part of SCF-Skp2. ► Drosophila SCF-Skp2 promotes growth independent of p27/Dap destruction.