Identification and characterization of a novel OCA-B isoform: Implicationsfor a role in B cell signaling pathways

OCA-B is a B lymphocyte-specific transcription coactivator that mediates ti ssue- and stage-restricted transcription of immunoglobulin genes. Earlier g enetic studies revealed that OCA-B is essential for germinal center formati on and production of secondary immunoglobulin isotypes. Biochemically purif ied OCA-B contains p35 and p34 isoforms, and a further analysis has now rev ealed that p35 is derived from a newly found isoform, p40. More importantly , it has been found that p35 is myristoylated in vivo and that this leads t o dramatic changes (including localization to membrane compartments) in its properties. These results suggest that the p35 isoform of OCA-B has functi ons distinct from those of the nuclear p34 and that it might be a component of a signaling pathway that is required for late-stage B cell development.