Comparative analysis of translation accuracy in an Escherichia coli and a mammalian cell-free system

Abstract

The effect of environmental stress on the accuracy of protein synthesis in an Escherichia coli and a rat brain cell-free system was investigated. Poly-U was translated in a rat brain and an E. coli cell-free extract under identical ionic conditions. The fidelity of translation, both in the E. coli and the rat brain extracts, was commensurate with what is known about the accuracy of translation in vivo. The incorporation of phenylalanine (code: UUU) and leucine (code: CUU, UUG or A) was measured at various Mg 2+ concentrations (3 to 22 m m), various pH's (6.6 to 8.6), various temperatures (23 to 42 °C), and in the presence or absence of 2.4% (v/v) ethanol. It was observed that (i) the accuracy of translation was generally higher in extracts from E. coli than from rat brain, and (ii) relative to that in E. coli, the translation fidelity in rat brain extracts was about 2 times more sensitive to ethanol, at least 5 times more sensitive to temperature, and at least 50 times more sensitive to pH. It was found that this differential sensitivity was not due to a differential behavior of the bacterial and the mammalian aminoacyl-tRNA synthetases under stress, but rather to the process of chain elongation itself. It is concluded that the accuracy of protein synthesis is more resistant to environmental stress in E. coli extracts than in extracts from at least one mammalian tissue.