The W element is a positive regulator of HLA-DRA transcription in various DR+ cell types.

The W and P elements are cis-acting transcriptional regulators of the human class II MHC gene HLA-DRA necessary for maximal promoter activity in DR+ B cells. Proteins that bind specifically to W may mediate promoter activity from a DNA segment containing W and P (W/P). In this report, we demonstrate that a -143 to -123 bp region that lacks P is sufficient to mediate the W elements function and to bind the W proteins W-B1 and W-B2 in the Raji B-lymphoblastoid cell line. In contrast to previous reports, we find that W/P is not a B cell-specific element; rather that its promoter activity parallels active transcription of the endogenous DRA gene. In addition, we show that tissue-restricted regulation by W/P is not correlated with the ubiquitous (W-B1) and lymphoid-specific (W-B2) distribution of the W binding proteins. We suggest that mechanisms in addition to binding to W may account for W/P-dependent transcriptional activation in DR+ cells.