Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, 112 Office and Lab Building, Ames, IA, 50011-3020, USA.|Present Address: Battelle Center for Mathematical Medicine, The Research Institute at Nationwide Childrens Hospital, Columbus, OH, 43205, USA.|Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, 112 Office and Lab Building, Ames, IA, 50011-3020, USA. jernigan@iastate.edu.