1. Department of Molecular, Cellular and Developmental Biology University of California Santa Barbara CA 93106‐9625 USA
2. Department of Microbiology and Environmental Toxicology University of California Santa Cruz CA 95064 USA
3. Centre for Immunology and Infection, Hull York Medical School and the Department of Biology University of York York YO10 5DD UK
4. Biomolecular Science and Engineering Program University of California Santa Barbara CA 93106‐9625 USA