[1] YALE UNIV, BOYER CTR MOLEC MED, DEPT MOLEC BIOPHYS & BIOCHEM, 295 CONGRESS AVE, NEW HAVEN, CT 06510 USA
[2] YALE UNIV, BOYER CTR MOLEC MED, HOWARD HUGHES MED INST, NEW HAVEN, CT 06510 USA
[3] UNIV ILLINOIS, DEPT PHYSIOL & BIOPHYS, CHICAGO, IL 60680 USA
[4] UNIV SASSARI, IST FISIOL GEN & CHIM BIOL, I-07100 SASSARI, ITALY