Fluorescence detected circular dichroism study of the anticodon loop of yeast tRNAPhe

Fluorescence detected circular dichroism (FDCD) measurements have been used to study the conformations of the anticodon loop of yeast phenylalanine tRNA. To our knowledge this is the first application of fluorescence detected circular dichroism. Much smaller amounts of tRNA are needed for the measurement of FDCD than for the conventionally measured circular dichroism. Furthermore, FDCD is specific for conformational changes near the anticodon loop. The FDCD measurements suggest a transition in the anticodon loop near 20 degrees in 0.01 M MgCl2-0.1 M NaCl (pH 7). This is followed by a broad transition from 30 to 60 degrees and finally a sharp melting at 75 degrees consistent with the absorbance detected melting of the entire tRNA. Removal of Mg2+ from the tRNA at 1 degrees causes nearly a factor of two decrease in the FDCD near 230 nm. This indicates a decrease in conformational rigidity in the anticodon loop on removal of Mg2+.