Denaturation of UGA suppressor tRNA Trp from E. coli

To help elucidate the structure of inactive tRNA Trp ( E. coli), reversible denaturation has been studied in the UGA suppressor tryptophan tRNA from strain CAJ64, which has an A. U instead of G. U pair in the dihydrouridine stem, and is more stable than the wild type tRNA. The Su + tRNA is half-denatured at 10 mM Na +, in the absence of magnesium, at 55°C, compared to 1M Na + for the wild type tRNA. Denatured Su + tRNA is less stable than the wild type, and ΔH r * in 5 mM Mg 2+ is 33 kcal/mole compared to 74 kcal/mole. These results favour the hypothesis that guanidine-24 pairs with a cytidine in the metastable denatured form.