Antifolate-resistant chinese hamster cells. Evidence from independently derived sublines for the overproduction of two dihydrofolate reductases encoded by different mRNAs.

A comparison by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the proteins synthesized by antifolate-sensitive (DC-3F) and -resistant (DC-3F/A3 and DC-3F/MQ19) Chinese hamster lung fibroblast cells has shown that an apparent molecular weight difference exists between the dihydrofolate reductases overproduced by the resistant sublines. Translation in a rabbit reticulocyte lysate system of polysomal and cytoplasmic mRNAs from the three sublines has shown that the overproduction of dihydrofolate reductase by resistant cells is accompanied by increased levels of dihydrofolate reductase-specific mRNA and that the different molecular weight forms of dihydrofolate reductase are encoded by their respective mRNAs.