Abstract
AbstractEquilibrium dialysis and electronic and nuclear resonance spectroscopy show that tRNA cooperatively binds divalent metal ions at very low concentrations (free metal concentration 3 × 10 −6 M). The first two methods show that different purified tRNAs have a very similar behavior, including initiator tRNAFmet. tRNAs with an extra arm in the clover‐leaf model, however, appear to have a slightly different behavior.The binding can be described in terms of two classes of sites. The cooperative association of divalent ions binding first does not parallel a cooperative change in the hyperchromism of the tRNA, while the non‐cooperative association of the second class of divalent ions corresponds to the concentrations needed to obtain a cooperative melting of the tRNA.The temperature dependence of the number of binding sites and of their binding constants is also presented.The nature of the divalent ion gives the following efficiency: for the cooperativity Co++>Mg++>Mn++ for the weak binding sites Mn++>Co++>Mg++
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