1. Department of Biochemistry and Molecular Biology, Brody School of Medicine, East Carolina University, 600 Moye Boulevard, Greenville, North Carolina 27858-4354, Department of Molecular and Cell Physiology, Medical School Hannover, D-30623 Hannover, Germany, and Department of Biological Science and Program in Molecular Biophysics, Florida State University, Tallahassee, Florida 32306-4370