Cell line specificity of regulatory regions of the β₃ gene. (A) The indicated constructs were transiently transfected into the β₃-expressing megakaryocytic cells K562, Dami, and HEL, into the β₃-expressing but nonmegakaryocytic cells HMEC-1 and WM793, and into non–β₃expressing cell lines CHO and 293 and assayed for luciferase activity. Fold increase and the standard error of the mean over the promoterless construct (background) are indicated. The number of times each construct was tested is shown in parentheses. The Materials and Methods describes how values were normalized. (B) Additional reporter gene assays were performed four times and are presented as the fold increase over the pGL-2-Promoter with the standard error of the mean.