Abstract
The mechanism by which certain divalent cations may cause toxic effects was studied by examining the in vitro response of certain transfer RNAs to the cations. Two Drosophila tRNAs, those for tyrosine and leucine, were examined by reversed-phase column 5 (RPC-5) chromatography in the presence of each of three metal ions, Zn 2+, Mg 2+, and Cd 2+. As Zn 2+ concentration increased, both tRNAs eluted at progressively higher ionic strengths and the isoacceptor patterns collapsed and then reappeared. In contrast, when either the Mg 2+ or the Cd 2+ concentration increased, both tRNAs eluted at lower ionic strengths and the resolution of each of the isoacceptors was reduced. The resolution of tRNA Tyr from tRNA Leu was best with Cd 2+ and poorest with Mg 2+. If the observed changes were caused by conformational changes, they should be reversed upon removal of the metal ion; this was found to be so. Recovery of the tRNA after chromatography was reduced with Zn 2+, presumably through nonspecific hydrolysis. One late-eluting leucyl-tRNA species was labile to incubation in the presence or absence of metal ion, followed by heating to 95°C. This same species was labile to Zn 2+ exposure in the absence of heating. We suggest that reversed-phase column 5 chromatography is useful for evaluation of the effect of divalent metal ions on tRNA conformation and that the effects of various toxic metal ions could be examined in this manner.
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