1. Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, MN 55455, USA
2. Department of Biological Chemistry, University of Michigan, Ann Arbor, MI 48109, USA
3. Department of Biochemistry, Max Planck Institute for Developmental Biology, Max-Planck-Ring 5, 72076 Tübingen, Germany
4. Department of Computational Medicine and Bioinformatics, University of Michigan, Ann Arbor, MI 48109, USA