title: Expression optimization and synthetic gene networks in cell-free systems.
abstract: Synthetic biology offers great promise to a variety of applications through the forward engineering of biological function. Most efforts in this field have focused on employing living cells, yet cell-free approaches offer simpler and more flexible contexts. Here, we evaluate cell-free regulatory systems based on T7 promoter-driven expression by characterizing variants of TetR and LacI repressible T7 promoters in a cell-free context and examining sequence elements that determine expression efficiency. Using the resulting constructs, we then explore different approaches for composing regulatory systems, leading to the implementation of inducible negative feedback in Escherichia coli extracts and in the minimal PURE system, which consists of purified proteins necessary for transcription and translation. Despite the fact that negative feedback motifs are common and essential to many natural and engineered systems, this simple building block has not previously been implemented in a cell-free context. As a final step, we then demonstrate that the feedback systems developed using our cell-free approach can be implemented in live E. coli as well, illustrating the potential for using cell-free expression to fast track the development of live cell systems in synthetic biology. Our quantitative cell-free component characterizations and demonstration of negative feedback embody important steps on the path to harnessing biological function in a bottom-up fashion.
authors.affiliation: Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Bethel Valley Road, Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA. karigdk@ornl.gov
authors.forename: David K
authors.initials: DK
authors.lastname: Karig
authors.forename: Sukanya
authors.initials: S
authors.lastname: Iyer
authors.forename: Michael L
authors.initials: ML
authors.lastname: Simpson
authors.forename: Mitchel J
authors.initials: MJ
authors.lastname: Doktycz
mesh_terms: D002474:Cell-Free System; D004926:Escherichia coli / Q000235:genetics; D025461:Feedback, Physiological; D005786:Gene Expression Regulation; D053263:Gene Regulatory Networks; D005813:Genes, Synthetic; D056968:Lac Repressors / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011506:Proteins / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism; D058615:Synthetic Biology / Q000379:methods
chemical_list: D056968:Lac Repressors; D011506:Proteins; D012097:Repressor Proteins; C034811:tetracycline resistance-encoding transposon repressor protein