[1] CASE WESTERN RESERVE UNIV, DEPT BIOL, CLEVELAND, OH 44106 USA
[2] MIT, DEPT BIOL, CAMBRIDGE, MA 02139 USA
[3] BIOZENTRUM, BASEL, SWITZERLAND
[4] MD ANDERSON HOSP & TUMOR INST, CYTOGENET & GENET DIV, HOUSTON, TX 77025 USA
[5] YALE UNIV, SCH MED DEPT BIOL, NEW HAVEN, CT 06520 USA