MITF expression and luciferase activity in IC-2 cells. (A) RT-PCR analysis of expression of MITF mRNA. PCR products from RNAs of NIH/3T3 cells (lanes 1 to 4) and from RNAs of IC-2 cells (lanes 5 to 8) were electrophoresed in 1.0% agarose gel containing ethidium bromide with HaeIII-digested Bluescript KS (−) plasmid DNA as a size marker (M). The amounts of RNA used for reverse transcription was 5.0 μg (lanes 1 and 5), 0.5 μg (lanes 2 and 6), 0.05 μg (lanes 3 and 7), and 0.005 μg (lanes 4 and 8), respectively. (B) Luciferase reporter gene promoter assay in IC-2 cells. The luciferase gene under control of the normal, deleted, or mutated p75 promoter was introduced into the IC-2 mast cell line with electroporation. All p75 promoters started from nt -250. Bars indicate the standard error of three assays.