Abstract
The species of RNA containing homologous sequences to a cDNA prepared against murine dihydrofolate reductase have been identified and partially characterized in a methotrexate-resistant subclone of the murine lymphoma L5178Y. Twelve discreet species have been identified by Northern blot analysis in the cytoplasm and four are associated with the nucleus. A majority of the cytoplasmic species are shown to be polyadenylated and range in size from approximately 0.8 to greater than 23.7 kb. Of the cytoplasmic species, four (i.e., 1.6, 1.3, 1.1, 0.8 kb) are found in the parental line as well as the MTX-resistant line. The 0.8-kb species is shown to be lacking a large portion of a 3′ noncoding region present on some of the higher-molecular-weight species. The 0.8- and 1.3-kb mRNAs containing dihydrofolate reductase coding sequences have been purified away from the other species and shown to translate to dihydrofolate reductase in an
in vitro protein synthesis system. It is concluded that within the dihydrofolate reductase gene-amplified cell line L5178Y C
3 there are multiple messenger RNAs coding for dihydrofolate reductase and that this multiple translatable mRNA phenomenon is not the result of gene amplification.