Timing of cyclin E gene expression depends on the regulated association of a bipartite repressor element with a novel E2F complex

Transient induction of the cyclin E gene in late G(1) gates progression into S. We show that this event is controlled via a cyclin E repressor module (CERM), a novel bipartite repressor element located near the cyclin E transcription start site. GERM consists of a variant E2F-binding site and a contiguous upstream AT-rich sequence which cooperate during G(0)/G(1) to delay cyclin E expression until late G(1). CERM binds the protein complex CERC, which disappears upon progression through G(0)-G(1) and reappears upon entry into the following G(1). CERC disappearance correlates kinetically with the liberation of the GERM module in vivo and cyclin E transcriptional induction, CERC contains E2F4/DP1 and a pocket protein, and sediments faster than classical E2F complexes in a glycerol gradient, suggesting the presence of additional components in a novel high molecular weight complex. Affinity purified CERC binds to CERM but not to canonical E2F sites, thus displaying behavior different from known E2F complexes. In cells nullizygous for members of the Rb family, CERC is still detectable and CERM-dependent repression is functional. Thus p130, p107 and pRb function interchangeably in CERC. Notably, the CERC-CERM complex dissociates prematurely in pRb(-/-) cells in correspondence with the premature expression of cyclin E. Thus, we identify a new regulatory module that controls repression of G(1)-specific genes in G(0)/G(1).