The Distribution of Transfer Ribonucleic Acid in Rabbit Reticulocytes

This study is a consideration of the condition and distribution of tRNA in rabbit reticulocytes. Levels of tRNA aminoacylation by 18 different amino acids were determined by assaying tRNA resistance to periodate oxidation. The levels range from 71% aminoacylation for tRNA accepting glycine to 97% for tRNAs accepting leucine and phenylalanine, with most values being close to 90 %. Amounts of tRNA accepting the 18 amino acids which are attached to ribosomes were determined. Yields of ribosomal material from known numbers of reticulocytes are equivalent to 100,000 80 S ribosomal monomers per cell. There are approximately 100,000 tRNA molecules per cell attached to these ribosomes, this being approximately one-quarter of the total reticulocyte tRNA content. The numbers of ribosomal tRNA molecules for the different amino acids vary widely and have no demonstrable relationship to rabbit hemoglobin amino acid composition or to the content of tRNA for these amino acids in whole reticulocytes. More than half of the total reticulocyte tRNA for leucine and phenylalanine is attached to ribosomes while only 10% of serine and alanine tRNA is ribosomal. The results are discussed in relation to the cycling of different kinds of tRNA during hemoglobin synthesis and to the possibility that the availability of certain tRNA species may limit the rate of hemoglobin synthesis in reticulocytes.