The 3 ' Ig kappa enhancer contains RNA polymerase II promoters: implications for endogenous and transgenic kappa gene expression

We have created a Ic transgene in which a polymerase (pol) III promoter rep laces the pol II promoter. Two independent transgenic lines show somatic hy permutation of the transgene in B cells from hyperimmunized mice. Both line s transcribe transgenes from the pol III promoter in the liver. However, in spleen and spleen B cell-derived hybridomas, they also transcribe mRNA fro m pol II promoters located within the 3' kappa enhancer of the preceding tr ansgene copy in a tandem transgene array. The findings demonstrate that in an array of multiple transgenes the expression (and somatic hypermutation) of an individual transgene copy must be considered in the context of the ot her copies. We also show that sequences around the 3' kappa enhancer in end ogenous genes are transcribed. The possible role of these promoters in endo genous kappa gene expression is discussed. An unrelated finding in this stu dy was a novel RNA splice in one hybridoma.