[1] UNIV TEXAS,DEPT ZOOL,AUSTIN,TX 78712
[2] RES INST MOLEC PATHOL,A-1030 VIENNA,AUSTRIA
[3] UNIV TEXAS,HOWARD HUGHES MED INST,DALLAS,TX 75235
[4] MRC,RADIOBIOL UNIT,DIDCOT,OXON,ENGLAND
[5] MAX PLANCK INST BIOL,IMMUNOGENET ABT,W-7400 TUBINGEN,GERMANY