Department of Genome Sciences, Howard Hughes Medical Institute, University of Washington, Seattle, WA 98195-5065, USA.|Department of Genome Sciences, Howard Hughes Medical Institute, University of Washington, Seattle, WA 98195-5065, USA.|Department of Genome Sciences, Howard Hughes Medical Institute, University of Washington, Seattle, WA 98195-5065, USA.|Department of Genome Sciences, Howard Hughes Medical Institute, University of Washington, Seattle, WA 98195-5065, USA.|Department of Genome Sciences, Howard Hughes Medical Institute, University of Washington, Seattle, WA 98195-5065, USA.