1. Whitehead Institute Center for Genome Research, MIT, Cambridge, MA 02139; Computer Science and Artificial Intelligence Laboratory, MIT, Cambridge, MA 02139
2. Computer Science and Artificial Intelligence Laboratory, MIT, Cambridge, MA 02139
3. Whitehead Institute Center for Genome Research, MIT, Cambridge, MA 02139.2 Computer Science and Artificial Intelligence Laboratory, MIT, Cambridge, MA 02139
4. Department of Biology, MIT, Cambridge, MA 02139