Effect of ethanol on the thermal stability of tRNA molecules.

The thermal denaturation of E. coli unfractionated tRNA in ethanol/water mixtures has been studied as a function of alcohol concentration in the water-rich region (mole fraction of co-solvent chi 2 less than 0.2). The results show that with increasing alcohol concentration the melting temperature of tRNA first reaches a minimum at an intermediate composition chi *2 approximately equal to 0.055 and then increases with increasing chi 2. The value of chi *2 is close to that at which structural changes in the mixture occur as inferred from compressibility and optical absorption measurements. The present experimental data support the assumptions that the dominant mechanism by which ethanol affects the thermal stability of tRNA molecules is through its effect on the structure of water.