X-box-binding proteins positively and negatively regulate transcription of the HLA-DRA gene through interaction with discrete upstream W and V elements.

Previous reports have identified that the class II box, consisting of the positive regulatory X and Y boxes, is important for expression of all class II major histocompatibility genes. In this paper, we identify additional sequences upstream from the class II box that regulate constitutive transcription of a human class II gene, HLA-DRA, in the B-lymphoblastoid cell line Raji. Using 5' promoter deletions, substitution mutants, and nuclease S1 protection assays, we mapped a positive element, called W, between -135 and -117 base pairs and a negative element, called V, from -193 to -179 base pairs. Sequence comparisons revealed that W and V share homology with the HLA-DRA X box situated downstream. Gel-mobility-shift assays confirmed that the Raji nuclear proteins that bound to W and V elements were competed with by an HLA-DRA X-box oligonucleotide. These results suggest that X-box-binding proteins mediate both positive and negative effects on transcription by means of interaction with multiple elements (W, V, and X) within the same HLA-DRA gene.