Emulsion based selection of T7 promoters of varying activity.

The ability to build and control complex biological systems is greatly enhanced by the generation of related parts with varying strengths. In this way, various parts can be strung together and the connectivity and expression levels can be matched for the desired system performance. Engineered gene circuits, both in vivo and in vitro, often utilize the T7 RNA polymerase in tandem with the T7 promoter for transcription. In this work, we describe the selection of T7 promoter variants of varying strength by emulsifying in vitro transcription with subsequent fluorescence activated cell sorting (FACS) to enrich for active promoters. Such variant promoters should be of use to synthetic biologists for both in vivo and in vitro applications.