B-CELL-SPECIFIC DNA-BINDING BY AN E47 HOMODIMER

B cells express a unique E-box-binding activity that contains basic he lix-loop-helix (bHLH) proteins encoded by the E2A gene. E2A proteins p lay a central role in immunoglobulin gene transcription and are also r equired for the generation of the B-lymphocyte lineage. In muscle, E2A proteins bind DNA as heterodimers with muscle-specific bHLH partners, such as MyoD and myogenin, and these heterodimers are thought to he b oth necessary and sufficient for muscle determination in cultured cell s, Our results indicate that in B cells, the bHLH partners for E2A pro teins are not B-cell-restricted proteins, but are the E2A proteins the mselves, UV cross-linking, gel purification, and the analysis of ''for ced heterodimers'' indicate that BCF1 is primarily a homodimer of the E2A protein E47. Since E47 is widely expressed, our results argue for a difference in the inherent DNA-binding properties of the E47 protein in B cells and may help explain the restricted B-lineage defect obser ved in E2A-deficient mice.