Presence of phosphorylatedO-ribosyl-adenosine In T-ψ-stem of yeast methlonine initiator tRNA

We report in this paper on isolation and characterization of two unknown nucleosides G* and A* located in the T-psi-stem of yeast methionine initiator tRNA, using the combined means of HPLC protocols, real time UV-absorption spectrum, and post-run mass spectrometry by electron impact or fast atom bombardment. The G* nucleoside in position 65 was identified as unmodified guanosine. The structure of the unknown A* in position 64 was characterized as an isomeric form of O-ribosyl-adenosine by comparison of its chromatographic, UV-spectral and mass spectrometric properties with those of authentic O-alpha-ribofuranosyl-(1"----2')-adenosine isolated from biosynthetic poly(adenosine diphosphate ribose). Our studies also brought evidence for the presence of a phosphorylmonoester group located on this new modified nucleoside A*, when isolated by ion exchange chromatography from enzymic hydrolysis of yeast initiator tRNAMet without phosphatase treatment.