1. Howard Hughes Medical Institute and Department of Biochemistry, University of Utah School of Medicine, Salt Lake City, Utah 84132, United States
2. Department of Biochemistry, University of Utah School of Medicine, Salt Lake City, Utah 84132, United States
3. Department of Chemistry and Biochemistry, University of California−Los Angeles, 607 Charles E. Young Drive East, Los Angeles, California 90095-1569, United States
4. Department of Biochemistry and Molecular Biology, School of Medicine, University of New Mexico Health Sciences Center, Albuquerque, New Mexico 87131, United States