Directed protein synthesis by messenger ribonucleoprotein and ribosomes from different mammalian species.

Abstract

There have been a number of attempts to direct protein synthesis using RNA particles containing specific genetic information. Although a variety of RNA preparations can stimulate polypeptide synthesis in bacterial cell-free systems, transfer of information has been demonstrable only with viral RNA or with synthetic polyribonucleotides.1-5 The ability to direct protein synthesis with either viral messenger RNA or with synthetic polyribonucleotides has given rise to the concept that bacterial ribosomes are nonspecialized structures which can synthesize polypeptides dictated by the messenger they happen to contain at a given time.6, 7 In mammalian systems there has been no unequivocal demonstration of directed protein synthesis with natural template RNA. Mammalian RNA preparations are capable of stimulating polypeptide synthesis by both bacterial and mammalian ribosomes, but a specific protein has not been identified in these systems.'2 Attempts to induce enzyme formation in tumor cells or to direct antibody synthesis with RNA have been inconclusive.3 14 Hendler15 has pointed out that an essential type of evidence for the firm establishment of the messenger concept would be the demonstration that a protein-synthesizing system of one species could be induced to make a specific protein characteristic of a completely different species, by the addition of RNA characteristic of the second species. For mammalian systems, reticulocyte ribosomes provide a favorable system for such studies. The hemoglobin obtained from various species differs significantly in physical properties, amino acid composition, and antigenicity. In cell-free systems, reticulocyte ribosomes synthesize globin, and the species specificity of the globin synthesized is associated with the ribosomes.16'-9 Presumably, the information controlling the specificity of the globin is encoded in a messenger RNA (mRNA) and this RNA could be used to study the possibility of directing protein synthesis. In the following report a ribonucleoprotein complex (mRNP) was obtained from deer reticulocyte ribosomes and combined with rabbit reticulocyte ribosomes. The resultant hybrid polyribosome complex was shown to synthesize polypeptide fragments characteristic of deer globin.