Transcription activity of MEL1 and MEL1S. (A) Transactivation of the luciferase gene via binding of MEL1 and MEL1S proteins to DNA consensus sequences. Transient transcriptional activation of the luciferase gene was measured with dual-luciferase reporter assay system. pGL3-promoter vector containing D1-CONS or D2-CONS was cotransfected into P19 cells along with either mock expression vector (pCMV), pCMV-MEL1, or pCMV-MEL1S and Renilla luciferase expression vector (pRL-TK). Relative firefly luciferase activity was measured in cell extracts and normalized with respect to Renilla luciferase activity. Each value represents the average obtained from 3 independent experiments. Bars indicate standard deviation errors. (B) Repressor activities of GAL4 DBD-fused MEL1 and MEL1S. P19 cells were cotransfected with the luciferase reporter vector of pGL3-p or pG5proLuc with 5 × the consensus GAL4 binding site (UAS) and with the mock expression vector (GAL4 DBD), GAL4 DBD-MEL1, GAL4 DBD-MEL1S, or positive control vector (pM3-VP16), respectively. After 48 hours of incubation, the cell extracts were analyzed for firefly luciferase activity, which was normalized using Renilla luciferase activity according to the manufacturer's instructions. Values of relative luciferase activity and error bars represent the means and standard deviations, respectively, of 3 separate experiments.