1. Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
2. HHMI, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
3. Department of Chemistry, University of Warwick, Coventry CV4 7AL, UK
4. Department of Biology, Colorado State University, Fort Collins, CO 80523
5. School of Life Sciences, University of Warwick, Coventry CV4 7AL, UK