1. Department of Computer Science , Durham, NC 27708, USA
2. Center for Genomic & Computational Biology , Durham, NC 27708, USA
3. Program in Computational Biology & Bioinformatics , Durham, NC 27708, USA
4. Department of Biostatistics & Bioinformatics, Department of Molecular Genetics and Microbiology, Department of Cell Biology, Duke University , Durham, NC 27708, USA