and NSP8 viral proteins. The RdRp TR-FRET Assay kit is designed to measure RdRp-mediated direct incorporation of biotinylated ATP into a double-stranded RNA substrate. The increase in TR-FRET signal is proportional to the amount of ATP incorporated in the RNA. This assay is ideal for high-throughput screening of enzyme inhibitors, to perform kinetic studies, or to accurately measure a drug EC50 . Conclusion TR-FRET is an ultra-low background technique allowing the measure of any reaction in which two labeled entities come in proximity. The main drawback of the technique is that it requires two optimized labeled entities, in addition to a low dynamic range. However, these drawbacks are offset by several advantages: * Small volumes * Homogeneous: no need for washing steps or for physical separation from the unbound entities * Robust, sensitive signal * Ultra-low background with high signal to noise ratio Figure 6: Simple Operation * Stable signal: use of lanthanide donor fluorophores minimizes photobleaching The growing commercial availability of ready-touse TR-FRET immunoassay kits has opened the technique to mainstream use. BPS Bioscience offers over 80 assay kits for drug discovery in the TR-FRET format with new products developed regularly. Optimized, validated, high-quality assay kits ensure reliable results, quickly. 25