Cln1 Background Information Cell cycle progression is controlled at a point late in G1 designated Start. Passage through Start requires the activity of the cyclin-dependent protein kinase Cdc28 (1,2). Transition from G1 to S phase requires the association of Cdc28 with members of the G1 cyclin family, including Cln1, Cln2 and Cln3 (also designated Daf1 or Whi1) (3). The G2 to M phase requires the M phase cyclins, Clb1 (also designated Scb1) and Clb2, as well as the G2 cyclins, Clb3 and Clb4 (4,5). The S phase cyclins Clb5 and Clb6 coordinate DNA replication with cytokinesis (6). Expression of the cyclins is controlled by Ubc9 and Cdc34 (also designated Ubc3 or Dna6) via ubiquitin-mediated proteolysis (7,8). Esp1 is released from an inhibitory complex with Pds1 and stimulates the cleavage of Scc1 from chromosomes, which mediates sister chromatid dissociation during the metaphase to anaphase transition of the cell cycle (9).
