MECHANISM OF DISCRIMINATION OF ESCHERICHIA-COLI TRNA(PHE) BY YEAST PHENYLALANYL-TRANSFER-RNA SYNTHETASE

Aminoacylation of homologous and heterologous tRNAs by yeast phenylalanyl-tRNA synthetase were investigated. Inactivation of the enzyme on aminoacylation of E. coli tRNA was due to pyrophosphorylation of the enzyme. Inorganic pyrophosphatase cleaves off the bound pyrophosphate and reactivates the enzyme. A similar effect was produced by homologous tRNA. Changes in the mechanism of the reaction with E. coli tRNA in comparison to yeast tRNA are linked to the sole significant difference in nucleotide sequence: G(20)-U-20 substitution. A putative mechanism of the enzyme inactivation on aminoacylation of heterologous tRNAs is discussed.