THE IG-KAPPA 3'-ENHANCER TRIGGERS GENE-EXPRESSION IN EARLY B-LYMPHOCYTES BUT ITS ACTIVITY IS ENHANCED ON B-CELL ACTIVATION

Ig kappa gene expression is controlled by two enhancers, one located w ithin the major intron (Ei) and the other located downstream of C-kapp a (E3'), Whereas loss of E3' has previously been shown to diminish kap pa expression, we show here that a rearranged kappa transgene lacking Ei is well expressed, even at the pre-a cell stage, This suggests that E3' alone might be sufficient to give properly regulated transcriptio n throughout B cell development, Indeed, we show that a transgene comp osed of a beta-globin reporter linked to E3' is expressed in a a cell- specific manner, becoming activated at the late pro-B to pre-a cell st age but with dramatically enhanced activity on B cell activation. Thus , E3' becomes active as a transcription enhancer at the stage when V-k appa-J(kappa) rearrangement is being initiated and is sufficient to yi eld an expression pattern in a linked reporter gene similar to that of fully rearranged kappa genes.