Laboratory for Biocomputing and Informatics, Graduate Program in Bioinformatics, and Department of Computer Science, Boston University, Boston, MA 02215, USA Laboratory for Biocomputing and Informatics, Graduate Program in Bioinformatics, and Department of Computer Science, Boston University, Boston, MA 02215, USA Laboratory for Biocomputing and Informatics, Graduate Program in Bioinformatics, and Department of Computer Science, Boston University, Boston, MA 02215, USA.