[1] NHLI,BETHESDA,MD 20014
[2] UNIV LEIDEN,DEPT BIOCHEM,LEIDEN,NETHERLANDS
[3] INST PASTEUR,PARIS,FRANCE
[4] INST BIOL PHYSICO CHIM,PARIS,FRANCE
[5] ROCHE INST MOLEC BIOL,NUTLEY,NJ 07110
[6] MIT,DEPT BIOPHYS,CAMBRIDGE,MA 02139
[7] BASEL INST IMMUNOL,BASEL,SWITZERLAND