Densitometric quantitation of CAT activity in TK^-ts13 cells cotransfected with pCMV-Ets-2 and pCAT B constructs containing various portions of the c-kit5′ flanking region. pCAT B RsaI-BamHI + pCMV ets-2 in antisense (as) orientation was employed as an additional control. Transfection reactions were normalized by use of PAP assays, as detailed in Materials and Methods. Mean ±SD of five different experiments, each performed in duplicate, are shown. CAT activity was normalized to the CAT control transfected cells that were arbitrarily set at 100%.