A sensitive assay which examines the effects of ATP level on the overall activity of a cell-free translation system in a protein synthesis is described. The translational activity of cell-free system was measured in terms of a rate of protein synthesis directed by the 'test' template. The test template encodes a photoluminescent protein, obelin accumulation was determined from the kinetic curves of obelin. The rate of obelin mRNA translation. Time-dependent nucleotide level measurements were conducted throughout the translation processes. It has been shown that the rate of translation decreases exponentially with the decrease of the ATP level. This fall in the overall translation rate is due in part to the mRNA becoming inactive in the translation process. This is not caused by degradation, this mRNA can be restored for translation in a fresh cell-free system by phenol treatment. The reported results provide evidence that the level of ATP unambiguously determines the translational activity of the system.