Unique function for carboxyl-terminal domain of Oct-2 in Ig-secreting cells

The activity of Ig gene promoters and enhancers Is regulated by two related transcription factors, Oct-1 (ubiquitous) and Oct-2 (B lineage specific), which bind the octamer motif (ATTTGCAT) present in these elements. As Ig pr omoter-binding factors, Oct-1 and Oct-2 each work together with a B lymphoc yte-specific cofactor OCA-B/OBF-1/Bob-1 that interacts with them through th eir POU (DNA-binding) domains. Because both can mediate Ig promoter activit y in B cells, there has been some question as to whether these two octamer- binding factors serve distinct functions in lymphocytes. We have shown prev iously that the silencing of B lymphocyte-specific genes In plasmacytoma X T lymphoma hybrids can be prevented by preserving Oct-2 expression. The pro nounced effect of this transcription factor on the phenotype of plasmacytom a X T lymphoma hybrids established a critical role for Oct-2 not only in ma intaining Ig gene expression, but in maintaining the overall genetic progra m of Ig-secreting cells. In the present study, we have explored the functio nal differences between Oct-1 and Oct-2 using chimeric Oct-1/Oct-2 proteins in cell fusion assays. Our results provide further evidence for an essenti al role for Oct-2 in Ig-secreting cells and identify the C-terminal domain of Oct-2 as responsible for its unique function in these cells.