Intron nine of the BARD1 gene confers estrogen responsiveness. MDAMB231 breast cancer cells were transfected with an ERα expression vector (ERα), a renilla control vector, and a reporter vector with a TATA sequence alone (TATA) or a TATA sequence combined with the 288 bp region of the BARD1 gene containing wild type DNA sequence (BARD) or one (mHS1, mHS2, mHS4) or three (mHS1,2,4) mutant ERE half sites as indicated in Panels A and B. Cells were treated with ethanol vehicle (−E2) or 10nM E2 (+E2) for 24 h. Data from four independent experiments were combined and are expressed as the mean in relative luciferase units (RLUs)±S.E.M. for all samples. Note that some error bars are too small to visualize. Statistical differences were determined using the Student's t-test as indicated by an asterisk in Panel A. Significant differences were determined by ANOVA in Panel B.