Jianjun Guo1,2, Xiaohan Yang3, David J. Weston3 and Jin-Gui Chen3*
1Department of Genetics, Harvard Medical School, Boston, Massachusetts 02114-2790, USA 2Department of Molecular Biology, Massachusetts General Hospital, Boston, Massachusetts 02114-2790, USA 3Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6422, USA