Expression of abbreviated mouse dihydrofolate reductase genes in cultured hamster cells.

Abstract
A number of abbreviated dihydrofolate reductase (DHFR) genes were constructed by using cloned mouse genomic and c[complementary]DNA sequences. These genes contain 1.0 kilobase of 5'' flanking genomic sequence and varying portions of the 3'' non-coding region. Two of the genes contain the first 2 introns of the DHFR gene; the other 3 lack introns. Transfection of DHFR-deficient Chinese hamster ovary cells with any of these constructed genes results in cells with the DHFR+ phenotype. Treatment of the transfectants with methotrexate, a folate antagonist, leads to the emergence of methotrexate-resistant colonies which amplified the transfected genes.