Transcriptional coactivator that specifically associates with either POU2F1/OCT1 or POU2F2/OCT2. It boosts the POU2F1/OCT1 mediated promoter activity and to a lesser extent, that of POU2F2/OCT2. It has no intrinsic DNA-binding activity. It recognizes the POU domains of POU2F1/OCT1 and POU2F2/OCT2. It is essential for the response of B-cells to antigens and required for the formation of germinal centers (PubMed:23045607). Regulates IL6 expression in B cells as POU2F2/OCT2 coactivator (PubMed:23045607). Interacts with POU2F1/OCT1 and POU2F2/OCT2; the interaction increases POU2F1 and POU2F2 transactivation activity. B-cell specific. In B cells, expression is highly increased upon activation by LPS or CpG. Ubiquitinated; mediated by SIAH1 or SIAH2 and leading to its subsequent proteasomal degradation. Mutants show severely reduced or absent germinal center B cells in the lung-draining lymphatic nodes when infected by influenza virus. Belongs to the POU2AF1 family.