OBF-1, A NOVEL B-CELL-SPECIFIC COACTIVATOR THAT STIMULATES IMMUNOGLOBULIN PROMOTER ACTIVITY THROUGH ASSOCIATION WITH OCTAMER-BINDING PROTEINS

Recent biochemical and genetic studies indicate that in addition to th e octamer-binding proteins Oct-1 and Oct-2, other B cell components ar e required for lymphoid-restricted, octamer site-mediated immunoglobul in gene promoter activity. Using a genetic screen in yeast, we have is olated a cell-derived cDNAs encoding Oct-binding factor 1 (OBF-1), a n ovel protein that specifically associates with Oct-1 and Oct-2. Bioche mical studies demonstrate that OBF-1 has no intrinsic DNA-binding acti vity and recognizes the POU domains of Oct-1 and Oct-2, but not those of Oct-4 and Oct-6. The OBF-1 mRNA is expressed in a highly cell-speci fic manner, being most abundant in B cells and essentially absent In m ost of the other cells or tissues tested. Furthermore, expression of O BF-1 in HeLa cells selectively stimulates the activity of a natural im munoglobulin promoter in an octamer site-dependent manner. Thus, OBF-1 has all the properties expected for a B cell-specific transcriptional coactivator protein.