Immunoglobulin kappa gene expression after stable integration. I. Role of the intronic MAR and enhancer in plasmacytoma cells.

Rearranged MOPC41 immunoglobulin kappa gene constructs have been stably introduced into cultured S194 mouse plasmacytoma cells to investigate the effects of deleting the intronic enhancer and/or matrix association region (MAR) on gene expression. Intact single-copy kappa genes containing 1.5 kilobase pairs of upstream and 8.5 kilobase pairs of downstream flanking sequences exhibited sensitivity to chromosome position effects and were expressed at a mean level of 27% relative to the endogenous kappa gene expression or only 6% with respect to the MOPC41 kappa mRNA levels in the tumor. Deletion of the intronic MAR led to a 4-fold decrease in expression, while deletion of both the MAR and enhancer led to an 11-fold decline. These effects were dampened by preselecting for integration into a transcriptionally poised chromatin location as demonstrated by linkage to a selectable marker which lacked both a MAR and an enhancer. Significantly, we found that sequences downstream of the poly(A) addition site compensated 150-fold for deletion of the intronic enhancer.