Cancer Research Institute Ghent (CRIG) 1 article published in JoVE Developmental Biology Structure-function Studies in Mouse Embryonic Stem Cells Using Recombinase-mediated Cassette Exchange Tim Pieters1,2,3,4, Lieven Haenebalcke1,2, Kenneth Bruneel1,2,4, Niels Vandamme1,2,4, Tino Hochepied1,2, Jolanda van Hengel5, Dagmar Wirth6, Geert Berx1,2,4, Jody J. Haigh7, Frans van Roy1,2,4, Steven Goossens1,2,3,4 1Department of Biomedical Molecular Biology, Ghent University, 2Inflammation Research Center, VIB, 3Center for Medical Genetics, Ghent University Hospital, 4Cancer Research Institute Ghent (CRIG), 5Department of Basic Medical Sciences, Faculty of Medicine and Health Sciences, Ghent University, 6Helmholtz Center for Infection Research, 7Mammalian Functional Genetics Laboratory, Division of Blood Cancers, Australian Centre for Blood Diseases, Department of Clinical Haematology, Monash University and Alfred Health Alfred Centre Proteins often contain multiple domains that can exert different cellular functions. Gene knock-outs (KO) do not consider this functional diversity. Here, we report a recombination-mediated cassette exchange (RMCE)-based structure-function approach in KO embryonic stem cells that allows for the molecular dissection of various functional domains or variants of a protein.