AbstractAll tRNA sequences so far known can be folded into a cloverleaf structure. Physical data and chemical reactions allow us to draw conclusions on secondary (cloverleaf) and tertiary structure.N‐oxidation of adenosine to adenosine‐1‐N‐oxide can be done with monoperphthalic acid in non‐base‐paired regions of polynucleotides and can be followed easily by changes in absorption of ultraviolet light. Thus this method can be used to determine the structure of tRNA's. A fingerprint of theN‐oxidation product of tRNAyeastPhereveals that all adenosine residues are protected except the 3′‐terminal adenosine and the three adenosine residues in or adjacent to the anticodon. On this basis a conformation of tRNAyeastPheis proposed. Similar tertiary structures can be constructed for the other tRNA's. In order to connect tertiary structure of a tRNA and recognition by its aminoacylating enzyme, the rate of aminoacylation, as a function of temperature, was measured. Neither changes in the anticodon nor specific changes at the 3′‐terminal adenosine abolish aminoacylation. Single crystals of tRNAyeastPhewere obtained from aqueous solutions upon addition of var
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