1. Department of Biological Chemistry; Weizmann Institute of Science; Rehovot 76100 Israel
2. Department of Molecular Genetics; Weizmann Institute of Science; Rehovot 76100 Israel
3. Department of Computer Science and Applied Mathematics; Weizmann Institute of Science; Rehovot 76100 Israel
4. Biological Services Department; Bioinformatics Unit, Weizmann Institute of Science; Rehovot 76100 Israel