Dissection of positive regulatory elements in the upstream region of theHLA-DBP1gene

We investigated the cis-acting sequences that function in the B-cell-specific expression of the HLA-DPB1 gene. Class II B major histocompatibility genes contain a conserved upstream sequence that is important in the expression of these genes. This region has been divided into three major elements, the W, X, and Y boxes. In this paper, we identified an additional positive regulatory element upstream from the DPB1 W box. Using 5' deletion mutants and a substitution mutant, we mapped a positive element, called the W' box, between -184 approximately -169 bp. Sequence comparison revealed that the W' box shares homology with the W box. Electrophoretic mobility shift assay confirmed that the W box binds proteins that also recognize the W' box. Furthermore, deletion and substitution mutants indicate that the W and W' boxes effectively enhance CAT activities only when the X and Y boxes exist.