pE2F-TA-Luc is designed to monitor the induction of E2F-mediated signal transduction pathways.E2F, a major target of the retinoblastoma gene (Rb), is a key regulator of cell-cycle checkpointsin mammalian cells (1–2). E2F plays a critical role in stimulating expression of genes encodinggrowth-promoting proteins (3), and is involved in regulating the expression of important genesduring cell proliferation (4–5). The E2F protein forms a heterodimer complex with the DP1protein, which binds to E2F response elements and initiates transcription of genes necessaryfor DNA replication. Studies have shown that deregulation of E2F results in a loss of cell-cyclecheckpoints—thereby predisposing cells to uncontrolled growth (1–5). pE2F-TA-Luc containsfour copies of the E2F enhancer element (6), located upstream of the minimal TA promoter, theTATA box from the herpes simplex virus thymidine kinase promoter (PTA). Located downstreamof PTA is the firefly luciferase reporter gene (luc). Upon binding of the E2F/DP1 complex to thecis-acting E2F enhancer element, transcription is induced and the reporter gene is activated.The luciferase coding sequence is followed by the SV40 late polyadenylation signal to ensureproper, efficient processing of the luciferase transcript in eukaryotic cells. A synthetic transcriptionblocker (TB) is located upstream of the cis-acting enhancer element. It is composed ofadjacent polyadenylation and transcription pause sites for blocking nonspecific transcription(7). The vector backbone also contains an f1 origin for single-stranded DNA production, a pUCorigin of replication, and an ampicillin resistance gene for propagation and selection in E. coli.