[1] UNIV LIBRE BRUXELLES, GENET LAB, B-1640 RHODE ST GENESE, BELGIUM
[2] UNIV CALIF SAN FRANCISCO, HOWARD HUGHES MED INST, SAN FRANCISCO, CA 94143 USA
[3] UNIV CALIF SAN FRANCISCO, DEPT PHYSIOL, SAN FRANCISCO, CA 94143 USA
[4] UNIV CALIF SAN FRANCISCO, DEPT BIOCHEM, SAN FRANCISCO, CA 94143 USA