MB0 is essential for induction of MYC target genes. Stable p53−/−/ARF−/− DKO MEFs expressing MYCER, MYCER∆MB0, MYCER∆MBI or empty vector were treated with 2 µM hydroxytamoxifen (OHT) for 0 or 12 h. Quantitative Real-Time RT-PCR (qRT-PCR) was performed as described in the Materials and Methods used to assess the levels of target genes Rcl, Hsp60 and Cdk4. Results were normalized to ß-actin levels and shown as fold induction over levels at 0 h. Open bars indicate mRNA levels prior to OHT treatment, closed bars indicate mRNA levels after 12 h OHT treatment. Asterisks indicate statistically significant increases in mRNA after treatment with OHT as determined by Student’s t-test (p < 0.05, n = 3 per treatment group). MYCER protein expression of the various constructs was determined by IB analysis.