INDUCIBLE EXPRESSION AND PHOSPHORYLATION OF COACTIVATOR BOB.1 OBF.1 IN T-CELLS/

BOB.1/OBF.1 is a transcriptional coactivator that is constitutively ex pressed in B cells and interacts with the Oct1 and Oct2 transcription factors. Upon activation of Jurkat T cells and primary murine thymocyt es with phorbol esters and ionomycin, BOB.1/OBF.1 expression and trans activation function were induced. BOB.1/OBF.1 was phosphorylated at Se r(184) both in vivo arid in vitro, and this modification was required for inducible activation. Mutation of Ser(184) also diminished transac tivation function in B cells, suggesting that the activating phosphory lation that is inducible in T cells is constitutively present in B cel ls. Thus, BOB.1/OBF.1 is a transcriptional coactivator that is critica lly regulated by posttranslational modifications to mediate cell type- specific gene expression.