Immunoglobulin κ gene expression after stable integration. II. Role of the intronic MAR and enhancer in transgenic mice

MOPC41 immunoglobulin κ gene constructs have been stably introduced into the mouse germ line to investigate the effects of deleting the conserved intronic sequences on gene expression. Intact κ genes containing 1.5 kilobase pairs of upstream and 8.5 kilobase pairs of downstream flanking sequences were highly expressed tissue-specifically, raising the total level of κ mRNA in spleens severalfold in most transgenic animals. This high expression was often accompanied by marked suppression of endogenous κ gene activity. Transgenes containing a deletion of the matrix association region (MAR) or both the MAR and enhancer were expressed tissue-specifically at mean levels only 2- and 3-fold lower, respectively, than that of intact transgenes. Therefore, while the intronic enhancer and MAR appear to play a quantitative role in gene expression, these sequences are not absolutely essential for transcriptional activation of rearranged κ genes in a normal developmental environment.