We have been doing research on the differential expression of one gene between two cell lines (A and B cell lines), with high expression in A cell line and no expression in B cell line. We found that ~250 bp in the promoter of the gene has its activity in A cell line, but no activity in B cell line. So we think the differential profiling of transcriptional factors between A band B cell lines decide whether the gene is expressed. However, I don’t know to find the transcriptional factors regulating the expression of the gene. Please give me some suggestions.