1. Department of Biophysics, University of Texas Southwestern Medical Center , Dallas, TX 75390, USA
2. McDermott Center for Human Growth and Development, University of Texas Southwestern Medical Center , Dallas, TX 75390, USA
3. Department of Biochemistry, University of Texas Southwestern Medical Center , Dallas, TX 75390, USA
4. Howard Hughes Medical Institute, University of Texas Southwestern Medical Center , Dallas, TX 75390, USA