Densitometric quantitation of CAT activity in stable, MYB-expressing TK^-ts13 cells cotransfected with a pCAT B plasmid containing various portions of the c-kit 5′ flanking region. CAT activity was normalized to the CAT positive-control transfected cells, which were arbitrarily set at 100%. Mean ±SD of five different experiments, each performed in duplicate are shown. Transfection reactions were normalized by use of PAP assays, as detailed in Materials and Methods.