RESEARCH ARTICLE The papain-like protease determines a virulence trait that varies among members of the SARS-coronavirus species Daniela NiemeyerID1,2,3, Kirstin Mo¨sbauer1, Eva M. KleinID2, Andrea Sieberg1,2, Robert C. Mettelman4, Anna M. Mielech4, Ronald DijkmanID5,6, Susan C. Baker4, Christian Drosten1,2,3☯*, Marcel A. Mu¨llerID1,2,3☯* 1 Institute of Virology, Charite´-Universita¨tsmedizin Berlin, corporate member of Freie Universita¨t Berlin, Humboldt-Universita¨t zu Berlin, and Berlin Institute of Health, Berlin, Germany, 2 Institute of Virology, University of Bonn Medical Centre, Bonn, Germany, 3 German Centre for Infection Research, associated partner Charite´, Berlin, Germany, 4 Department of Microbiology and Immunology, Loyola University of Chicago, Maywood, IL, United States of America, 5 Institute of Virology and Immunology, Bern & Mittelha¨usern, Switzerland, 6 Department of Infectious Diseases and Pathobiology, University of Bern, Bern, Switzerland ☯ These authors contributed equally to this work. *