The ability to detect an infectious agent in a widespread epidemic is crucial to the success of quarantine efforts in addition to sensitive and accurate screening of potential cases of infection from patients in a clinical setting. Enabling testing outside of sophisticated laboratories broadens the scope of control and surveillance efforts, but also requires robust and simple methods that can be used without expensive instrumentation. Here we report a method to identify SARS-CoV-2 (COVID-19) virus RNA from purified RNA or cell lysis using loop-mediated isothermal amplification (LAMP) using a visual, colorimetric detection. This test was additionally verified using RNA samples purified from respiratory swabs collected from COVID-19 patients in Wuhan, China with equivalent performance to a commercial RT-qPCR test while requiring only heating and visual inspection. This simple and sensitive method provides an opportunity to facilitate virus detection in the field without a requirement for complex diagnostic infrastructure.. CC-BY 4.0 International license It is made available under a author/funder, who has granted medRxiv a license to display the preprint in perpetuity.is the (which was not peer-reviewed) The copyright holder for this preprint .

The ability to specifically attach chemical probes to individual proteins represents a powerful approach to the study and manipulation of protein function in living cells. It provides a simple, robust and versatile approach to the imaging of fusion proteins in a wide range of experimental settings. However, a potential drawback of detection using chemical probes is the fluorescence background from unreacted or nonspecifically bound probes. In this report we present the design and application of novel fluorogenic probes for labeling SNAP-tag fusion proteins in living cells. SNAP-tag is an engineered variant of the human repair protein O6-alkylguanine-DNA alkyltransferase (hAGT) that covalently reacts with benzylguanine derivatives. Reporter groups attached to the benzyl moiety become covalently attached to the SNAP tag while the guanine acts as a leaving group. Incorporation of a quencher on the guanine group ensures that the benzylguanine probe becomes highly fluorescent only upon labeling of the SNAP-tag protein. We describe the use of intramolecularly quenched probes for wash-free labeling of cell surface-localized epidermal growth factor receptor (EGFR) fused to SNAP-tag and for direct quantification of SNAP-tagged β-tubulin in cell lysates. In addition, we have characterized a fast-labeling variant of SNAP-tag, termed SNAPf, which displays up to a tenfold increase in its reactivity towards benzylguanine substrates. The presented data demonstrate that the combination of SNAPf and the fluorogenic substrates greatly reduces the background fluorescence for labeling and imaging applications. This approach enables highly sensitive spatiotemporal investigation of protein dynamics in living cells.

T cell receptor (TCR)-induced apoptosis of thymocytes is mediated by calcium-dependent expression of the steroid receptors Nur77 and Nor1. Nur77 expression is controlled by the transcription factor myocyte enhancer factor 2 (MEF2), but how MEF2 is activated by calcium signaling is still obscure. Cabin1, a calcineurin inhibitor, was found to regulate MEF2. MEF2 was normally sequestered by Cabin1 in a transcriptionally inactive state. TCR engagement led to an increase in intracellular calcium concentration and the dissociation of MEF2 from Cabin1, as a result of competitive binding of activated calmodulin to Cabin1. The interplay between Cabin1, MEF2, and calmodulin defines a distinct signaling pathway from the TCR to the Nur77 promoter during T cell apoptosis.

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A naturally occurring split intein from the dnaE gene of Synechocystis sp. PCC6803 (Ssp DnaE intein) has been shown to mediate efficient in vivo and in vitro transsplicing in a foreign protein context. A cis-splicing Ssp DnaE intein construct displayed splicing activity similar to the trans-splicing form, which suggests that the Nand C-terminal intein fragments have a high affinity interaction. An in vitro trans-splicing system was developed that used a bacterially expressed N-terminal fragment of the Ssp DnaE intein and either a bacterially expressed or chemically synthesized intein C-terminal fragment. Unlike artificially split inteins, the Ssp DnaE intein fragments could be reconstituted in vitro under native conditions to mediate splicing as well as peptide bond cleavage. This property allowed the development of an on-column trans-splicing system that permitted the facile separation of reactants and products. Furthermore, the trans-splicing activity of the Ssp DnaE intein was successfully applied to the cyclization of proteins in vivo. Also, the isolation of the unspliced precursor on chitin resin allowed the cyclization reaction to proceed in vitro. The Ssp DnaE intein thus represents a potentially important protein for in vivo and in vitro protein manipulation.Protein splicing elements, termed inteins (1), catalyze their own excision from a primary translation product with the concomitant ligation of the flanking protein sequences (reviewed in Refs. 2-4). Inteins catalyze three highly coordinated reactions at the N-and C-terminal splice junctions (5, 6): 1) an acyl rearrangement at the N-terminal cysteine or serine; 2) a transesterification reaction between the two termini to form a branched ester or thioester intermediate; and 3) peptide bond cleavage coupled to cyclization of the intein C-terminal asparagine to free the intein. Inteins have been engineered to be versatile tools in protein purification (7-13), protein ligation (9, 10, 12, 14 -18), and in the formation of cyclic proteins and peptides (11,19,20). However, the ligation and cyclization approaches were limited by the need to generate an N-terminal cysteine and/or C-terminal thioester intermediate in vitro.In addition to inteins engineered to trans-splice (21-24), a naturally occurring split intein was recently identified in the dnaE gene encoding the catalytic subunit of DNA polymerase III of Synechocystis sp. PCC6803 (25). The N-terminal half of DnaE, followed by a 123-amino acid intein sequence, and the C-terminal half, preceded by a 36-amino acid intein sequence, are encoded by two open reading frames located more than 745 kilobases apart in the genome. When co-expressed in Escherichia coli, the two DnaE-intein fragments exhibited protein trans-splicing (25). In this report we have further investigated the cis-and trans-splicing activities of the Ssp DnaE intein in a foreign protein context. Furthermore, novel methods were developed that allow the on-column ligation of protein fragments as well as the in vivo and in vitro cyclization of p...