1 Department of Virology, Research Institute for Microbial Diseases, Osaka University, Osaka, 565-0871, Japan. Electronic address: tkobayashi@biken.osaka-u.ac.jp.
2 Department of Biology, Indiana University, Bloomington, USA. Electronic address: jtpatton@iu.edu.
3 Department of Medicine, University of Cambridge, Addenbrooke's Hospital,Cambridge CB2 0QQ, United Kingdom. Electronic address: ud207@medschl.cam.ac.uk.