Intronic positioning maximizes co-expression and co-amplification of nonselectable heterologous genes

The overproduction of heterologous gene products in mammalian cells is often a prerequisite for studies of protein structure, function, and therapeutic efficacy. We report that recombinant fusion of a nonselectable reporter template into the intronic sequences of an amplifiable minigene gives dramatically enhanced co-expression efficiency in stable, primary transformants. Further incremental selective pressure for marker gene amplification results in the rapid acquisition of very high expression levels from the intronically positioned reporter. Nested within a constitutively expressing gene, these templates can be independently regulated at moderate gene dosage levels. Intronic positioning may therefore be of general utility for a variety of recombinant studies.