Undecagold cluster modified tRNA(Phe) from Escherichia coli and its activity in the protein elongation cycle.

An undecagold cluster (Au11) of molecular mass 6200Da was attached to the 3-(3-amino-3-carboxypropyl)uridine at position 47 of tRNA(Phe) from Escherichia coli. This modified tRNA can be enzymically aminoacylated with phenylalanine in the reaction catalyzed by phenylalanyl-tRNA synthetase. Au11-labeled Phe-tRNA(Phe) forms a ternary complex with the elongation factor Tu.GTP and is active in poly(U)-dependent poly(phe) synthesis. The Au11 modification does not hinder the specific binding of tRNA to distinct ribosomal binding sites or the precise positioning of the aminoacyl and peptidyl residues in the peptidyltransferase center, and does not impair the translocation. The modified tRNA is suitable for the identification of ribosomal binding sites by scanning transmission electron microscopy and for crystallographic studies of the 70S ribosome at different states of the protein-elongation cycle.