title: Riboswitch-Based Reversible Dual Color Sensor.
abstract: Riboswitches are RNA-based "sensors" that utilize chemically induced structural changes in the 5'-untranslated region of mRNA to regulate expression of downstream genes. Coupling a specific riboswitch with a reporter gene system translates chemical detection by the cell into a quantifiable reporter protein signal. For the majority of reporter gene systems, the readout signal is only expressed in the presence of the target analyte. This makes it difficult to determine the viability and localization of the uninduced biosensor when it is used for "real-word" applications. To address this problem, we developed a dual-color reporter comprising elements of the E. coli fimbriae phase variation system: recombinase FimE controlled by a synthetic riboswitch and an invertible DNA segment (fimS) containing a constitutively active promoter placed between two fluorescent protein genes. Without an analyte, the fluorescent reporter constitutively expressed green fluorescent protein (GFPa1). Addition of the analyte initiated translation of fimE causing unidirectional inversion of the fimS segment and constitutive expression of red fluorescent protein (mKate2). Thus, the sensor is always fluorescent, but its color is determined by detection of a specific analyte. We demonstrate that the recombinase-based dual-color reporter can be successfully applied to monitor the activation of a theophylline synthetic riboswitch that was used as our model system. To show the feasibility of the FimE recombinase-based system to serve as a reporter for monitoring activation of multiple synthetic riboswitches and, therefore, expand the applicability of the system, we tested a number of previously developed synthetic riboswitches responsive to different analytes. We show that the dual-color reporter system can be successfully used to monitor activation of M6 and M6″ riboswitches responsive to ammeline and pyrimido[4,5-d]pyrimidine-2,4-diamine, respectively, and a 2,4,6-trinitrotoluene-responsive riboswitch developed in this study. We also demonstrate that the system can be reversed by HbiF recombinase-mediated fimS inversion to the initial state of the fluorescent reporter, creating a resettable and reusable cell-based sensor.
authors.affiliation: 711th Human Performance Wing, Airman Systems Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base , Wright-Patterson AFB, Ohio 45433, United States.|The Henry M. Jackson Foundation , 6720A Rockledge Drive, Bethesda, Maryland 20817, United States.
authors.forename: Svetlana V
authors.identifier: 0000-0001-9051-1397
authors.initials: SV
authors.lastname: Harbaugh
authors.affiliation: 711th Human Performance Wing, Airman Systems Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base , Wright-Patterson AFB, Ohio 45433, United States.|UES, Inc. , 4401 Dayton-Xenia Road, Dayton, Ohio 45432, United States.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Goodson
authors.affiliation: 711th Human Performance Wing, Airman Systems Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base , Wright-Patterson AFB, Ohio 45433, United States.
authors.forename: Kateri
authors.initials: K
authors.lastname: Dillon
authors.affiliation: 711th Human Performance Wing, Airman Systems Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base , Wright-Patterson AFB, Ohio 45433, United States.
authors.forename: Sarah
authors.initials: S
authors.lastname: Zabarnick
authors.affiliation: 711th Human Performance Wing, Airman Systems Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base , Wright-Patterson AFB, Ohio 45433, United States.
authors.forename: Nancy
authors.initials: N
authors.lastname: Kelley-Loughnane
mesh_terms: D015374:Biosensing Techniques / Q000379:methods*; D004926:Escherichia coli / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics; D045522:Recombinases / Q000235:genetics / Q000378:metabolism; D058928:Riboswitch / Q000235:genetics*
chemical_list: D045522:Recombinases; D058928:Riboswitch
keywords: biosensor; dual-color detection; recombinase; riboswitch