Lead-catalyzed cleavage of yeast tRNA super(Phe) mutants

Yeast tRNA super(Phe) lacking modified nucleotides undergoes lead-catalyzed cleavage between nucleotides U17 and G18 at a rate very similar to that of its fully modified counterpart. The rates of cleavage for 28 tRNA super(Phe) mutants were determined to define the structural requirements of this reaction. The cleavage rate was found to be very dependent on the identity and correct positioning of the two lead-coordinating pyrimidines defined by X-ray crystallography. Nucleotide changes that disrupted the tertiary interactions of tRNA super(Phe) reduced the rate of cleavage even when they were distant from the lead binding pocket. However, nucleotide changes designed to maintain tertiary interactions showed normal rates of cleavage, thereby making the reaction a useful probe for tRNA super(Phe) structure.