The promoter and 5' flanking sequences controlling human B29 gene expression

The product of the B-cell-specific B29 gene (B29, Ig beta, CD79b) is essential for Ig-mediated B-cell activation via the B-cell antigen receptor complex (BCR) on human and murine B lymphocytes. To better understand the regulation of this pivotal gene, we have analyzed the human genomic DNA sequence upstream of the B29 ATG start codon for transcriptional control activity. The human B29 gene lacks either a TATA or a CAAT box and transcription is initiated at multiple sites. The minimal promoter of the human B29 gene is contained within a 193-bp region 5′ of these multiple start sites. This minimal promoter exhibits B-cell-specific activity and contains SP1, ETS, OCT, and IKAROS/LYF-1 transcription factor motifs. All these motifs are strikingly conserved in sequence and placement relative to the previously characterized murine B29 promoter. Additional upstream gene segments dramatically affected B29 minimal promoter activity. A newly identified motif called the B29 conserved sequence (BCS), found upstream of both human and murine B29 promoters, appears to stimulate B29 transcription through a novel mechanism. A single BCS had little effect either on the minimal B29 promoter or on a heterologous promoter. Instead, the BCS stimulated transcription by counteracting 5′ negative regulatory DNA sequences that block the activity of the B29 minimal promoter in its absence. These findings indicate that B29 gene expression is controlled by the complex interplay of positive and negative regulatory elements.