Transcriptional coactivator that specifically associates with either OCT1 or OCT2. It boosts the OCT1 mediated promoter activity and to a lesser extent, that of OCT2. It has no intrinsic DNA-binding activity. It recognizes the POU domains of OCT1 and OCT2. It is essential for the response of B-cells to antigens and required for the formation of germinal centers. Reduced activation of Bob1-deficient B cells following antigenic stimulation is often reported. The action of Bob1 on B cell maturation and tolerance could be mediated by effects on B cell activation, in part by regulating the expression of immunosuppressive miRNAs. Bob1 has long been considered a B cell‐specific factor that interacts with the transcription factors Oct1 and Oct2 to enhance octamer‐dependent transcription. Bob1 can directly bind to and transactivate the promoters of Bcl6 and Btla.