INVESTIGATION OF NUCLEIC ACID SECONDARY STRUCTURE BY MEANS OF CHEMICAL MODIFICATION WITH A CARBODIIMIDE REAGENT .2. REACTION BETWEEN N-CYCLOHEXYL-N'-BETA-(4-METHYLMORPHOLINIUM)ETHYLCARBODIIMIDE AND TRANSFER RIBONUCLEIC ACID

The reaction between the carbodiimide reagent, N-cyclohexyl-N′-β-(4-methylmorpholinium)ethylcarbodiimide, and Escherichia coli transfer ribonucleic acid has been investigated. The extent of reaction was examined under a variety of conditions of temperature, salt type, and concentration, and reagent and ribonucleic acid concentration. The presence of magnesium ions was found to reduce the extent of reaction considerably. The results have been interpreted in the light of the transfer ribonucleic acid nucleotide sequence data and the physicochemical data that are available. The results are consistent with the existence of three forms of tertiary structure, all based upon the cloverleaf type of secondary structure. The biologically active form is a very compact structure in which most of the limited number of unpaired nucleotides that are exposed are in the anticodon loop. The loss of two of the biological activities of transfer ribonucleic acid following the carbodiimide modification has been examined. In the absence of magnesium ions, the amino acid acceptor activities are all lost rapidly. In the presence of this divalent cation, the pattern of loss varies very much from one amino acid accepting species to another. The effect of the carbodiimide reaction on the binding of aminoacyl transfer ribonucleic acid to ribosomes has also been studied. © 1969, American Chemical Society. All rights reserved.