1 Laboratoire des Protéines Complexes, CNRS URA 1334, Université de Tours, 37032 Tours, France, Micromass UK Limited, 3 Tudor Road, Altrincham, Cheshire WA14 5RZ, UK, Equipe d'Ecophysiologie, Station Biologique, UPMC-CNRS-INSU, BP 74, 29682 Roscoff, France, Biology Department, Brookhaven National Laboratory, Upton, New York 11973, Department of Zoophysiology, Institute of Biological Sciences, Aarhus University, 8000 Aarhus C, Denmark, and Department of Biochemistry and Molecular Biology, Wayne State University School of Medicine, Detroit, Michigan 48201.