The CellSensor® dhfr(E2F)-bla NIH 3T3 Cell Line contains a beta-lactamase reporter gene under control of the E2F/DP1 binding sequence from the DHFR gene promoter, stably integrated into NIH 3T3 cells. This cell line is a clonal population isolated by flow cytometry in response to 10% newborn bovine serum. This cell line has been tested for assay performance under variable conditions, including DMSO concentration, cell number, stimulation time, and substrate loading time, and validated for Z-factor using newborn bovine serum. Additional data using alternate stimuli are shown. The G1/S cell-cycle checkpoint controls the passage of eukaryotic cells from the first gap phase (G1) into the DNA synthesis phase (S). Two cell-cycle kinases, CDK4/6-cyclin D and CDK2-cyclin E, and the transcription complex that includes Rb and E2F, are pivotal in controlling this checkpoint. During G1, the Rb-HDAC repressor complex binds to the E2F-DP1 transcription factors, inhibiting downstream transcription. Phosphorylation of Rb by CDK4/6 and CDK2 dissociates the Rb-repressor complex, permitting transcription of S-phase genes encoding for proteins that amplify the G1-to-S switch and that are required for DNA replication. Many different stimuli exert checkpoint control, including TGFβ, DNA damage, contact inhibition, replicative senescence, and growth factor withdrawal. Academic and non-profit customers, please inquire for special pricing.