We examined the homology between polysomal polyadenylated ribonucleic acid (mRNA) populations of hepatoma 252, a tumor which is deficient in the synthesis of plasma proteins, and those of normal and regenerating rat liver. Hybridization of polyadenylated mRNA populations with homologous or heterologous complementary deoxyribonucleic acids showed that mRNA from total and free polysomes from hepatoma 252 lack sequences which are present in normal or regenerating liver. Although there are obvious differences in the abundance of sequences between tumor and normal or regenerating liver polysomal mRNA, we did not detect, with the techniques used in this work, tumor-specific sequences. Analysis of hybridization curves using derivative plots did not reveal the presence in tumor mRNA of a high complexity class not present in normal liver. We conclude that alterations in mRNA populations of free and total polysomes of this tumor primarily reflect processes of genetic restriction rather than the derepression of previously unexpressed genes.
The nucleotide sequence of a low molecular weight RNA coded by bacteriophage T4 (and previously identified as species alpha) has been determined. The molecule is of particular biological interest for its associated biosynthetic properties. This RNA is 76 nucleotides in length, contains eight modified bases, and can be arranged in a cloverleaf configuration common to tRNAs. The anticodon sequence is UGU, which corresponds to the threonine-specific codons ACA G. The nucleotide sequence was determined primarily by nearest-neighbor analysis of RNA synthesized in vitro using [alpha-32P]nucleoside triphosphates. Using the single-strand specific nuclease S1, two in vivo labeled half-molecules were generated and analysed. This information together with restrictions imposed by nearest-neighbor data, provided a unique linear sequence of nucleotides with the features of secondary structure common to tRNA molecules.
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