Stoichiometry of GTP hydrolysis in a poly(U)-dependent cell-free translation system. Determination of GTP/peptide bond ratios during codon-specific elongation and misreading.

The stoichiometry of GTP hydrolysis during peptide elongation in the processes of codon-specific translation and misreading of polyuridylic acid was determined in a cell-free system in which all ribosomes were active in peptide synthesis. Ribosomes carrying oligophenylalanine presynthesized on poly(U) covalently bound to Sepharose were used. In the codon-specific translation of poly(Phe) on poly(U)-Sepharose at optimal Mg2+ concentration (6 mM MgCl2), the ratio of GTP cleaved to Phe polymerized was found to be about 2 (+/- 0.1). Under the same conditions but during misreading (elongation of polyleucine on poly(U)-Sepharose) the GTP/Leu ratio increased 10 times (from 16 to 25 in different experiments).