[1] MCMASTER UNIV, DEPT PATHOL, MOLEC VIROL & IMMUNOL PROGRAM, HAMILTON L8N 3Z5, ONTARIO, CANADA
[2] MCMASTER UNIV, DEPT BIOL, HAMILTON L8N 3Z5, ONTARIO, CANADA
[3] DUPONT CO, EXPT STN, WILMINGTON, DE 19898 USA
[4] SK&F LABS, DEPT MOLEC GENET, PHILADELPHIA, PA 19101 USA