1. Department of Biochemistry and Cellular and Molecular Biology; The University of Tennessee; Knoxville 37996 TN
2. National Laboratory of Solid State Microstructure and Department of Physics; Nanjing University; No. 22, Hankou Road Nanjing 210093 People's Republic of China
3. Graduate School of Genome Science and Technology; University of Tennessee and Oak Ridge National Laboratories; Knoxville 37996 TN