The 3′ Igκ enhancer contains RNA polymerase II promoters: implications for endogenous and transgenic κ gene expression

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Abstract
We have created a κ transgene in which a polymerase (pol) III promoter replaces the pol II promoter. Two independent transgenic lines show somatic hypermutation of the transgene in B cells from hyperimmunized mice. Both lines transcribe transgenes from the pol III promoter in the liver. However, in spleen and spleen B cell-derived hybridomas, they also transcribe mRNA from pol II promoters located within the 3′ κ enhancer of the preceding transgene 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 other copies. We also show that sequences around the 3′ κ enhancer in endogenous genes are transcribed. The possible role of these promoters in endogenous κ gene expression is discussed. An unrelated finding in this study was a novel RNA splice in one hybridoma.