An essential octamer motif in the mb-1 (Ig alpha) promoter

The mb-1 (Ig alpha) gene is B cell-specific and expressed throughout B cell maturation. In combination with B29 (Ig beta) and surface immunoglobulin m b-1 comprises the B cell receptor complex (BCR). The murine mb-1 promoter h as been characterized to depend on the trans-acting transcription factors; Sp1, ets, Ikaros, and EBF for full promoter activity. These trans-acting fa ctors are also involved in the regulation of mb-1's closely related heterod imeric partner, B29. However, octamer transcription factors 1 and 2 (Oct-1 and Oct-2) are also necessary for full B29 promoter activity while they are not known to be required for mb-1 promoter activity. Here, we show that th e octamer transcription factors bind a degenerate octamer consensus sequenc e within the mb-1 promoter. Like B29, the mb-1 octamer-binding, motif inter acted with both ubiquitously expressed Oct-1 and the B cell-specific Oct-2 transcription factors. Furthermore, the interaction of Oct-1 and Oct-2 cont ributed to the regulation of the mb-1 promoter as site-directed mutations w ithin the octamer motif substantially reduced its activity. These data conf irm that octamer factor interactions and function contribute to the full tr anscriptional activity of the mb-1 promoter. (C) 2000 Elsevier Science Ltd. All rights reserved.