The Role of tRNA in Regulation

Abstract

tRNA molecules were discovered about 20 years ago and the subsequent clarification of their role in protein biosynthesis developed from two different approaches. One approach, stemming from thermodynamic considerations, led Lipmann (1941) to postulate that amino acids had to be activated before they could be polymerized. Subsequently, Hoagland et al. (1957) discovered the formation of high-energy anhydride bonds between ATP and the carboxyl groups of amino acids. These authors reported that a soluble protein fraction from rat liver catalyzed the exchange of ³²P with ATP, a reaction enhanced severalfold by the addition of pure amino acids. This protein fraction was shown to contain an RNA species of low molecular weight, called soluble RNA or sRNA, which binds amino acids and these bound amino acids could be transferred to proteins. Second, from another view, Crick (1958) pointed out that nucleic acids could not form highly specific templates for binding the side chains of the amino acids. Nucleic acids lack both the charges required to bind amino acids and the hydrophobic cavities necessary for interaction with the aliphatic amino acids. Moreover, Crick noted that a particular sequence of bases can provide a highly specific pattern of sites for hydrogen bonding and suggested that each amino acid is combined with a special adaptor,which is in turn capable of forming a definite pattern of hydrogen bonding with a nucleic acid template. It was soon realized that the RNA discovered by Hoagland et al. (1957) could perform just such a function. Subsequent research has shown that sRNA, now known as transfer RNA or tRNA, is the adaptor for amino acids in protein synthesis and that tRNA plays a central role in the transfer of information from DNA to proteins.