1. Department of Biochemistry and Molecular Biology, The University of Texas, Medical Branch, Galveston, TX 77555, USA
2. Sealy Center for Structural Biology and Molecular Biophysics, The University of Texas Medical Branch, Galveston, TX 77555, USA
3. Department of Molecular Microbiology and Immunology, Oregon Health and Science University, Portland, OR 97239, USA
4. Department of Molecular and Cellular Biology, Baylor College of Medicine, TX 77030, USA