Multiple motifs regulate the B-cell-specific promoter of the B29 gene

The B-cell-specific B29 and mb1 genes code for covalently linked proteins (B29 or Ig beta and mb1 or Ig alpha, respectively) associated with membrane immunoglobulins in the antigen receptor complex on B cells. We have functionally analyzed the upstream region of the B29 gene and have identified a 164-bp region which comprises the minimal promoter responsible for B-cell-specific transcription. Linker scanning mutagenesis of this minimal promoter has established that both the previously identified octamer motif and a DNA motif that binds an unknown protein factor are critical for B29 gene expression in a pre-B-cell and B-cell line. Further mutations showed that binding motifs for Ets, microB/LyF1, and Sp1 also significantly contributed to the overall activity of the minimal B29 promoter. However, the relative contribution of certain motifs to promoter activity was different in a pre-B versus a B-cell line. The microB/LyF1 motif was necessary for full promoter activity in the pre-B cells but was not required in the B cells.