Center for Bioinformatics and Computational Biology, University of Maryland, College Park, MD 20742, USA. cole@cs.umd.edu|Center for Bioinformatics and Computational Biology, University of Maryland, College Park, MD 20742, USA. cole@cs.umd.edu|Center for Bioinformatics and Computational Biology, University of Maryland, College Park, MD 20742, USA. cole@cs.umd.edu