A comparison of the fluorescence of the Y base of yeast tRNA-Phe in solution and in crystals.

The fluorescence properties of the Y base of yeast tRNA-Phe are known to be quite sensitive to the environment. The fluorescence lifetime of the Y base in yeast tRNA-Phe is identical in orthorhombic crystals and in the mother liquor from which these crystals are grown. It is 10% higher than the lifetime observed in dilute solutions of tRNA. This small change is a solvent effect due to isopropyl alcohol in the crystallization medium. Isopropyl alcohol does not change the accessibility of the chromophore of the Y base as measured by iodide quenching rates in solution. The accessibility in intact tRNA-Phe is much less than in a ribonuclease digest. Thus, within the limits of the sensitivity of the method, the Y chromophore occupies the same environment in solution and in the crystal and it must be at least partially buried.