UBC Theses and Dissertations

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UBC Theses and Dissertations

Selective cleavage of transfer ribonucleic acid Mitchel, Ronald E. J.

Abstract

All guanosine residues in tRNA react with glyoxal to form adducts. No breakage of phosphodiester bonds of the tRNA occurs during the reaction. These adducts contain vicinal hydroxyl functions which can complex with borate or be oxidized by periodate to give N-formyl guanosine residues. The latter in tRNA afford little if any protection against attack by RNase T₁. The rate of cleavage at guanosine by this enzyme is slowed by the glyoxal adduct. Cleavage at guanosine by RNase T₂ occurs at less than 10% of the residues under conditions where the enzyme splits all other phosphodiester bonds. When borate is complexed with the adduct, cleavage by RNase T₁ is practically eliminated. The protection of tRNA with this borate glyoxal adduct followed by digestion with RNase T₁ offers a method to selectively cleave tRNA at inosine and 1-methyl guanosine residues The sequential removal of nucleotides from tRNA by snake venom phosphodiesterase (exonuclease) is completely stopped by a guanosine residue possessing a glyoxal-borate complex. Protection of pG with this adduct prevents removal of the phosphate by snake venom 5'-nucleotidase.

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