Interaction of rabbit reticulocyte ribosomes with bacteriophage f1 mRNA and of Escherichia coli ribosomes with rabbit globin mRNA

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Abstract
The behavior of a prokaryotic mRNA in a eukaryotic ribosome binding system and a eukaryotic mRNA in a prokaryotic ribosome binding system was compared. Using 32P- and 125I-labeled bacteriophage f1 mRNA, it was shown that rabbit reticulocyte 80S ribosomes can protect specific sequences from pancreatic RNase digestion, including those sequences protected by E. coli ribosomes. E. coli ribosomes fail to protect any region of 125I-labeled globin mRNA. Iodination of the mRNA had little or no effect on the specificity of binding or protection by the ribosomes of either system. The eukaryotic and prokaryotic systems differ markedly in the ability of the small ribosomal subunits to protect mRNA from nuclease digestion. The regions of phage f1 mRNA protected by E. coli 30S subunits are virtually identical to those protected by the 70S ribosomes. Rabbit reticulocyte 40S subunits protect substantially larger fragments of mRNA from nuclease digestion than do the 80S ribosomes. These 40S-protected fragments are specific in the case of globin mRNA and overlap the shorter region protected by the 80S ribosomes. The 40S-protected fragments of phage f1 mRNA were extremely heterogeneous, reflecting perhaps an important difference between the initial interactions made by these 2 mRNAs with the ribosomes.