University Hospital of the Ruhr-University of Bochum 1 article published in JoVE Genetics Measurement of BK-polyomavirus Non-Coding Control Region Driven Transcriptional Activity Via Flow Cytometry Johannes Korth1,2, Helene Sertznig2, Siegfried Moyrer2, Adrian Atilla Nicolas Doevelaar2,3, Timm Henning Westhoff3, Nina Babel3, Oliver Witzke4, Andreas Kribben1, Ulf Dittmer2, Marek Widera2 1Department of Nephrology, University of Duisburg-Essen, University Hospital Essen, 2Institute for Virology, University of Duisburg-Essen, University Hospital Essen, 3Center for Translational Medicine, Medical Department I, Marien Hospital Herne, University Hospital of the Ruhr-University of Bochum, 4Department of Infectious Diseases, University of Duisburg-Essen, University Hospital Essen Hufelandstr In this manuscript, a protocol is presented to perform FACS-based measurement of BK-polyomavirus transcriptional activity by using HEK293T cells transfected with a bidirectional reporter plasmid expressing tdTomato and eGFP. This method further allows to quantitatively determine the influence of novel compounds on viral transcription.