[1] HARVARD UNIV, SCH MED, DEPT BIOL CHEM, BOSTON, MA 02115 USA
[2] UNIV MINNESOTA, SCH MED, DEPT LAB MED & PATHOL, MINNEAPOLIS, MN 55455 USA
[3] HARVARD UNIV, SCH MED, DANA FARBER CANC INST, BOSTON, MA 02115 USA
[4] HARVARD UNIV, DEPT BIOCHEM & MOLEC BIOL, CAMBRIDGE, MA 02138 USA