1. Department of Pharmacology, Howard Hughes Medical Institute, University of Washington School of Medicine, Seattle, WA, USA
2. Department of Biochemistry, Howard Hughes Medical Institute, University of Washington School of Medicine, Seattle, WA, USA
3. Current address: Janelia Farm Research Campus, Howard Hughes Medical Institute, Ashburn, VA, USA
4. Department of Genome Sciences, University of Washington School of Medicine, Seattle, WA, USA