Summary Agonist-promoted G-protein coupled receptor (GPCR) endocytosis and recycling plays an important role in many signaling events in the cell. However, the approaches that allow fast and quantitative analysis of such processes still remain limited. Here we report an improved labeling approach based on the genetic fusion of a Fluorogen Activating Protein (FAP) to a GPCR and binding of a sulfonated analog of the malachite green (MG) fluorogen to rapidly and selectively label cell surface receptors. Fluorescence microscopy and flow cytometry demonstrate that this dye does not cross the plasma membrane, binds with high affinity to a dL5** FAP-GPCR fusion construct, activating tagged surface receptors within seconds of addition. The ability to rapidly and selectively label cell surface receptors with a fluorogenic genetically encoded tag allows quantitative imaging and analysis of highly dynamic processes like receptor endocytosis and recycling.

Limited experimental tools are available to study the consequences of collisions between DNA-bound molecular machines. Here, we repurpose a catalytically inactivated Cas9 (dCas9) construct as a generic, novel, targetable protein–DNA roadblock for studying mechanisms underlying enzymatic activities on DNA substrates in vitro. We illustrate the broad utility of this tool by demonstrating replication fork arrest by the specifically bound dCas9–guideRNA complex to arrest viral, bacterial and eukaryotic replication forks in vitro.

The most promising F508del-CFTR corrector, VX-809, has been unsuccessful as an effective, stand-alone treatment for CF patients, but the rescue effect in combination with other drugs may confer an acceptable level of therapeutic benefit. Targeting cellular factors that modify trafficking may act to enhance the cell surface density of F508-CFTR with VX-809 correction. Our goal is to identify druggable kinases that enhance F508del-CFTR rescue and stabilization at the cell surface beyond that achievable with the VX-809 corrector alone. To achieve this goal, we implemented a new high-throughput screening paradigm that quickly and quantitatively measures surface density and total protein in the same cells. This allowed for rapid screening for increased surface targeting and proteostatic regulation. The assay utilizes fluorogen-activating-protein (FAP) technology with cell excluded and cell permeant fluorogenic dyes in a quick, wash-free fluorescent plate reader format on live cells to first measure F508del-CFTR expressed on the surface and then the total amount of F508del-CFTR protein present. To screen for kinase targets, we used Dharmacon's ON-TARGET plus SMARTpool siRNA Kinase library (715 target kinases) with and without 10 μM VX-809 treatment in triplicate at 37 °C. We identified several targets that had a significant interaction with VX-809 treatment in enhancing surface density with siRNA knockdown. Select small-molecule inhibitors of the kinase targets demonstrated augmented surface expression with VX-809 treatment.