About the Authors
Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts, United States of America
Division of Virology, MRC National Institute for Medical Research, London, United Kingdom
The authors have declared that no competing interests exist.
PJ, JPS, and JMC conceived the study. JPS retrieved initial sequences and PJ performed bioinformatics analyses. PJ, JPS, and JMC analyzed the results and wrote the paper.