The effect of monovalent cations on a cell-free transcription–transla-
tion (TX–TL) system is examined using a luciferase assay. It is found that
the potency for all ions analyzed here is in the order Rb+ > K+ > Cs+ >
Na+ ≈ Li+ > (CH3)4N+, where Rb+ is most efficient at promoting TX–TL and the ions of Li+, Na+, and (CH3)4N+ exhibit an inhibitory effect. Similar promotion/ inhibition effects are observed for cell-free TL alone with an mRNA template.