Molecular biology of severe acute respiratory syndrome coronavirus John Ziebuhr The worldwide epidemic of severe acute respiratory syndrome (SARS) in 2003 was caused by a novel coronavirus called SARS-CoV. Coronaviruses and their closest relatives possess extremely large plus-strand RNA genomes and employ unique mechanisms and enzymes in RNA synthesis that separate them from all other RNA viruses. The SARS epidemic prompted a variety of studies on multiple aspects of the coronavirus replication cycle, yielding both rapid identification of the entry mechanisms of SARS-CoV into host cells and valuable structural and functional information on SARS-CoV proteins. These recent advances in coronavirus research have important implications for the development of anti-SARS drugs and vaccines. Addresses Institute of Virology and Immunology, University of Wu¨ rzburg, Versbacher Str. 7, 97078 Wu¨ rzburg, Germany e-mail: