Clb3 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 Udc3 or Dna6) via ubiquitin-mediated proteolysis (7,8).
