Cloned complementary deoxyribonucleic acid probes for untranslated messenger ribonucleic acid components of mouse sarcoma ascites cells

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Abstract
Mouse sarcoma ascites cells contain several abundant m[messenger]RNA species that occur to a large extent in an untranslated state. RNA preparations enriched in these species were used as starting material to construct recombinant plasmids. Cloned plasmids bearing sequences homologous to 4 of the untranslated mRNA species were identified by translation of hybrid-selected material. These plasmids, as well as a recombinant plasmid derived from chick .alpha.-actin mRNA, were used as probes for the estimation of mRNA levels in polyribosomes and in small ribonucleoprotein (RNP) particles of the ascites cells. Considerable amounts of the mRNA molecules belonging to the untranslated species were present in polyribosomes as well as in mRNP. The actin mRNA, on the other hand, was present almost exclusively in polyribosomes. The distribution obtained by the hybridization assay resembled those estimated by translation of the same RNA preparations in cell-free systems. The mRNA molecules of a given species engaged in translation in the cells and those present as untranslated RNP particles are equally effective in cell-free translation systems.