OcaB Is Required for Normal Transcription and V(D)J Recombination of a Subset of Immunoglobulin κ Genes

OcaB, a transcriptional coactivator also known as Bob-1 or OBF-1, was isolated on the basis of its ability to enhance transcription of immunoglobulin (Ig) genes in vitro. Paradoxically, OcaB−/− mice showed no apparent deficiency in Ig gene transcription, only cellular immune defects including absence of germinal centers (GC) and decreased numbers of immature B cells; the genes targeted by OcaB were not determined. Here we report that OcaB is essential for V(D)J recombination of a subset of Igκ genes. We show that OcaB modulates recombination by directly enhancing Igκ gene transcription in vivo.