Synthetic cells can mimic the intricate complexities of live cells, while mitigating the level of noise that is present natural systems; however, many crucial processes still need to be demonstrated in synthetic cells to use them to comprehensively study and engineer biology. Here we demonstrate key functionalities of synthetic cells previously available only to natural life: differentiation and mating. This work presents a toolset for engineering combinatorial genetic circuits in synthetic cells. We demonstrate how progenitor populations can differentiate into new lineages in response to small molecule stimuli or as a result of fusion, and we provide practical demonstration of utility for metabolic engineering. This work provides a tool for bioengineering and for natural pathway studies, as well as paving the way toward the construction of live artificial cells.

A teaching laboratory experiment is described where students prepare in vitro transcription reactions of a fluorescent RNA aptamer, named Broccoli, and observe the production of the aptamer in real-time on a fluorescence plate reader. Alternate visualization methods with minimal costs are also described for laboratories lacking this instrumentation. Two optional experiments are also described. Optional Experiment 1 involves purification of RNA transcription reactions using a commercial spin column kit and having students correlate cleanup kit yield with transcribed aptamer fluorescence. Optional Experiment 2 involves running a polyacrylamide gel of the transcription reaction with a ladder, followed by staining with (Z)-4-(3′,5′-difluoro-4′-hydroxybenzylidene)-2-methyl-1-(2″,2″,2″-trifluoroethyl)-1H-imidazol-5-(4H)-one (DFHBI-1T) (selective for Broccoli) and a second stain with SYBR Gold (nonselective, allowing for simultaneous visualization of Broccoli and ladder). This experiment has the practical advantage of enabling aptamer visualization in laboratories without a fluorescence spectrometer or plate reader, as well as the pedagogical benefit of demonstrating specific activation of the fluorescence of a small molecule by an RNA aptamer in another context (gel staining). Each experiment allows students to perform straightforward, easily understood teaching laboratory experiments, including key concepts in cellular imaging, and RNA biochemistry widely employed in biochemical research.

Efficient cell-free protein expression from linear DNA templates has remained a challenge primarily due to template degradation. Here we present a modified T7 RNA polymerase promoter that acts to significantly increase the yields of both transcription and translation within in vitro systems. The modified promoter, termed T7Max, recruits standard T7 RNA polymerase, so no protein engineering is needed to take advantage of this method. This technique could be used with any T7 RNA polymerase- based in vitro protein expression system. Unlike other methods of limiting linear template degradation, the T7Max promoter increases transcript concentration in a T7 transcription reaction, providing more mRNA for translation.

Background Efficient cell-free protein expression from linear DNA templates has remained a challenge primarily due to template degradation. In addition, the yields of transcription in cell-free systems lag behind transcriptional efficiency of live cells. Most commonly used in vitro translation systems utilize T7 RNA polymerase, which is also the enzyme included in many commercial kits. Results Here we present characterization of a variant of T7 RNA polymerase promoter that acts to significantly increase the yields of gene expression within in vitro systems. We have demonstrated that T7Max increases the yield of translation in many types of commonly used in vitro protein expression systems. We also demonstrated increased protein expression yields from linear templates, allowing the use of T7Max driven expression from linear templates. Conclusions The modified promoter, termed T7Max, recruits standard T7 RNA polymerase, so no protein engineering is needed to take advantage of this method. This technique could be used with any T7 RNA polymerase- based in vitro protein expression system.

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Synthetic minimal cells are a class of small liposome bioreactors that have some, but not all functions of live cells. Here, we report a critical step towards the development of a bottom-up minimal cell: cellular export of functional protein and RNA products. We used cell penetrating peptide tags to translocate payloads across a synthetic cell vesicle membrane. We demonstrated efficient transport of active enzymes, and transport of nucleic acid payloads by RNA binding proteins. We investigated influence of a concentration gradient alongside other factors on the efficiency of the translocation, and we show a method to increase product accumulation in one location. We demonstrate the use of this technology to engineer molecular communication between different populations of synthetic cells, to exchange protein and nucleic acid signals. The synthetic minimal cell production and export of proteins or nucleic acids allows experimental designs that approach the complexity and relevancy of natural biological systems.

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