Development of a new measurement standard for synthetic circuit design

Large-scale engineering of biological circuits requires reliable measurements of genetic parts and a deep understanding of interactions between synthetic circuits and the host cell. However, the widespread adoption of non-physical units of measurement makes it difficult to parameterize synthetic parts and cellular context, which hinders the efforts to model multi-component synthetic circuits in a predictable way. Here we present a new measurement standard in which DNA- and RNA- binding proteins fused with spectrally well-separated fluorescent proteins are used to visualize plasmid and mRNA simultaneously. By combining quantitative fluorescence microscopy with a customized image processing pipeline, we are able to quantify promoter copy number, RNA production and protein abundance at the single cell level. This allows us to determine biophysical parameters of genetic devices, such as the RNA polymerase flux of a standard promoter. We also show that the new measurement standard can be further applied to investigate the transcriptional power of bacteria cells.