[1] UNIV MICHIGAN,HOWARD HUGHES MED INST,DEPT HUMAN GENET,ANN ARBOR,MI 48109
[2] UNIV ALABAMA,GREGORY FLEMING JAMES CYST FIBROSIS RES CTR,BIRMINGHAM,AL 35233
[3] UNIV ALABAMA,DEPT PHYSIOL & BIOPHYS,BIRMINGHAM,AL 35233
[4] HOSP SICK CHILDREN,RES INST,TORONTO M5G 1X8,ONTARIO,CANADA
[5] UNIV MICHIGAN,SCH MED,HOWARD HUGHES MED INST,DEPT BIOL CHEM,ANN ARBOR,MI 48109