Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America.|Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America.|Departments of Biophysics and Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America.|Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America.|Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America.|Departments of Biophysics and Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America.|Departments of Biophysics and Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America.|Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America, Departments of Biophysics and Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America.