IDENTIFICATION AND STRUCTURAL CHARACTERIZATION OF O-BETA-RIBOSYL-(1''-]2')-ADENOSINE-5''-PHOSPHATE IN YEAST METHIONINE INITIATOR TRANSFER-RNA

We report in this paper on the complete structure determination of the modified nucleotlde A*, now called Ar(p), that was previously identified in yeast methionine initiator tRNA as an isomeric form of O-ribosyl-adenoslne bearing an additional phosphoryl-monoester group on its ribose2 moiety. By using the chemical procedure of periodate oxidation and subsequent β-elimlnation with cyclohexylamine on mono- and dinucleotides containing Ar(p), we characterized the location of the phosphate group on the C-5″ of the ribose2 moiety, and the linkage between the two riboses as a (1″→2′)-glycosidic bond. Since the structural difference between phosphatase treated Ar(p) and authentic O-α-ribosyl-(1″→2′)-adenoslne from poly(ADP-Ribose) was previously assigned to an isomeric difference in the ribose2-ribose1 linkage, the (1″2′)-glycosidic bond of Ar(p) was deduced to have a β-spatial configuration. Thus, final chemical structure for Ar(p) at the position 64 in yeast initiator tRNAMet has been established as O-β-ribosyl-(1″→2′)adenosine-5″-phosphate. This nucleotide is linked by a 3′,5′-phosphodiester bond to G at the position 65. © 1990 Oxford University Press.