Abstract
The phosphorescence spectra and phosphorescence excitation spectra of tRNAVal, tRNATyr, tRNAPhe and total tRNA from Escherichia coli have been rcorded at 77° K in the presence and absence of magnesium ions. The main phosphorescence of these tRNA species originates from sulfur‐containing nucleosides which have very high phosphorescence quantum yields as compared to their oxygenated analogs.The phosphorescence of 4‐thiouridine excited at 345 nm has a very short lifetime (about) 3 msec). The phosphorescence spectrum and quantum yield of 4‐thiouridine in tRNATyr are shown to differ from those of 4‐thiouridine in tRNAVal and tRNAPhe (lower quantum yield and red‐shift). These differences are attributed to interactions between two adjacent 4‐thiouridine residues in tRNATyr. The phosphorescence spectrum of 2‐methylthio‐N6‐(Δ2‐isopentenyl)‐adenosine excited at 280 nm has a characteristic shape which is observed for many adenine on the phosphorescence spectra of the tRNA species used in this study. The phosphorescence quantum yields of thionucleosides in tRNATyr are increased in the presence of Mg2+ions.Phosphorescence measurements provide a convenient method to determine the presence of and identify sulfur‐containing nucleosides in pure species of tRNA. The possible use of thionucleoside phosphorescence to study conformational changes in tRNA and interactions involving tRNA molecules is suggested.
Published Version
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