Enzymatic Incorporation of Amino Acid from Aminoacyl Soluble Ribonucleic Acid into Ribosomal Ribonucleic Acid and Ribosomal Protein

Abstract

The incorporation of amino acids into ribonucleic acid associated with cytoplasmic ribonucleoprotein particles has been observed in incubations with intact and cell-free systems from ascitcs cells (1, 2) and cell-free preparations from rat liver (3). Further studies in this laboratory demonstrated that amino acid incorporation into the RNA component of ribonucleoprotein occurs when microsomes or ribosomes are incubated with free 14C-amino acids or aminoacyl sRNA1 in the presence of the appropriate enzyme preparations (4). “Pulse labeling” techniques (2) and time-rate studies (3) suggested that ribosomal RNA may play an intermediary role in amino acid incorporation into proteins. These results and others indicating that the polynucleotide portion of aminoacyl sRNA is reversibly incorporated into ribonucleoprotein (58) are consistent with this suggestion. The incorporation of amino acid or aminoacyl sRNA into ribosomal RNA might therefore represent a stage in the formation of template-bound intermediates in the biological polymerization of amino acids. It appeared important to investigate the nature of the radioactive nonprotein material bound to ribosomes and to determine whether an interaction between aminoacyl sRNA and RNA of the ribosome could be demonstrated. This communication describes studies on the factors required for the formation of ribosomal RNA-bound amino acids, some of the properties of the product or products formed, and their possible participation as particle-bound intermediates in amino acid incorporation. The evidence presented below suggests the existence of a complex involving low molecular weight ribosomal RNA and prptides.