T7 transcriptional promoters can control well the amount of RNA produced during transcription-translation with the PURE system and do so consistently across different gene sequences. However, T7 transcriptional promoters are poor in regulating the production of protein. Conversely, ribosome binding sites greatly impact the synthesis of protein, but the effect is inconsistent between different sequences, likely reflecting complications arising from the structure of the mRNA. Further, the variability in expressed protein is significantly greater than that of expressed mRNA. Nevertheless, a computational model that takes into account the variability of transcription-translation and data on the exploited biological parts can be used to select for a subset of sequences with desired activity.