Partial melting of the segment around pseudouridine in yeast 5S RNA

Abstract

Pseudouridine in yeast 5S RNA was modified with 4-bromomethyl-7-methoxycoumarin(BMC). Temperature dependence of fluorescence intensity was measured at various concentrations of Mg 2+ and K + cations. Hyperchromicity was also measured. At 100mM KCl and 10mM Mg 2+, fluorescence intensity decreased with temperature as free BMC except a plateau at 45°C. Withdrawal of Mg 2+ from the buffer resulted in a large quenching at 20°C and showed a gradual increase of fluorescence intensity with temperature, indicating a partial melting of the segment around pseudouridine. The temperature range agrees with the low melting temperature shown by hyperchromicity. In 10mM KCl solution, the effects are more exaggerated.