High fidelity of guanine translation in a plasmid-directed in vitro system.

The extent of misreading of individual bases in the first or second codon position has been measured in vitro in a simplified plasmid-directed coupled system in which natural messenger translation is restricted to the formation of the N-terminal di- or tripeptide. Experiments were performed under conditions of competition between cognate and noncognate tRNAs in the presence of streptomycin to maximize the frequency of reading errors. A striking lack of susceptibility to mistranslation of guanine, as compared to the other 3 bases, was observed.