LAUSR

Genetically engineered photoreceptors enable unrivaled control over gene expression. Previously, we ported the Synechocystis PCC 6803 CcaSR two‐component system, which is activated by green light and deactivated by red, into Escherichia coli, resulting in a sensor with a sixfold dynamic range. Later, we optimized pathway protein expression levels and the output promoter sequence to decrease transcriptional leakiness and to increase the dynamic range to approximately 120‐fold. These CcaSR v 1.0 and v 2.0 systems have been used for precise quantitative, temporal, and spatial control of gene expression for a variety of applications. Recently, other workers deleted two PAS domains of unknown function from the CcaS sensor histidine kinase in a system similar to CcaSR v 1.0. Here we apply these deletions to CcaSR v 2.0, resulting in a v 3.0 light sensor with an output four times less leaky and a dynamic range of nearly 600‐fold. We demonstrate that the PAS domain deletions have no deleterious effect on CcaSR green light sensitivity or response dynamics. CcaSR v 3.0 is the best‐performing engineered bacterial green light sensor available, and should have broad applications in fundamental and synthetic biology studies.