1. LEDSS, Chimie Bioorganique, UMR CNRS 5616, Université Joseph Fourier, BP 53, 38041 Grenoble Cedex 9, France, International Agency for Research on Cancer, 150 Cours Albert Thomas, 69372 Lyon Cedex 08, France, and Molecular Epidemiology Unit, Algernon Firth Building, University of Leeds, Leeds LS2 9JT, U.K.