Department of Biochemistry and Molecular Biology, University of Georgia, Athens, GA 30602, USA. ffzhou@csbl.bmb.uga.edu|Department of Biochemistry and Molecular Biology, University of Georgia, Athens, GA 30602, USA. ffzhou@csbl.bmb.uga.edu|Department of Biochemistry and Molecular Biology, University of Georgia, Athens, GA 30602, USA. ffzhou@csbl.bmb.uga.edu