Affiliation: | (1) California Institute of Technology, Division of Biology 147-75, 91125 Pasadena, CA, USA;(2) Present address: Institute for Molecular Biology I, University of Zürich, CH-8093 Zürich, Switzerland;(3) Present address: Department of Biology, McGill University, 1205 Dr. Penfield Ave., H3A1B1 Montreal, Canada |