GENE STRUCTURE AND CHARACTERIZATION OF THE MURINE HOMOLOG OF THE B-CELL-SPECIFIC TRANSCRIPTIONAL COACTIVATOR OBF-1

The B cell-specific activity of immunoglobulin (Ig) gene promoters is to a large extent mediated by the conserved octamer motif ATTTGCAT. Th is requires the DNA binding octamer factors Oct-1 and/or Oct-2, as wel l as an additional B cell-restricted non-DNA binding cofactor. We rece ntly cloned such a coactivator specific for Oct-1 or Oct-2 from human B cells and called it OBF-1. Here we report the isolation and characte rization of the murine homologue. Full-length cDNA clones as well as g enomic clones were isolated and the gene structure was determined. The deduced protein sequence shows that the mouse protein has an identica l length, is likewise proline rich and shows 89% overall identity to t he human protein. The OBF-1 gene is expressed in a very highly B cell- specific manner and is transcribed in cells representative of all stag es of B cell differentiation, including the earliest ones., We show th at OBF-1 interacts in the absence of DMA with the POU domain of Oct-1 or Oct-2 and also with the general transcription factors TBP and TFIIB . Furthermore, we demonstrate that although OBF-1 efficiently activate s promoter octamer sites, it does not activate enhancer octamer sites.