Associates with cyclin-dependent kinases (CDKs) and plays an essential role in the regulation of the cell cycle that affects plant growth rate. May inhibit both the G1/S and G2/M phases. Interacts with CDKA-1 (PubMed:10100639, PubMed:11319029, PubMed:9276444, PubMed:20706207). Interacts with CDKB1-1, CDKB1-2 and CDKB2-1 (PubMed:11319029, PubMed:9276444, PubMed:11432958). Interacts with CYCD2-1 and At4g14310 (PubMed:20706207). Plants overexpressing CKS1 show reduced leaf size and root growth rates resulting from an increase of the cell-cycle duration with an equal extension of both G1 and G2 phases and a shortening of the meristem. Belongs to the CKS family.