2 Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Building C1, Room C-103, Boston, Massachusetts 02115.
3 University of California, Los Angeles, 611 Charles E. Young Drive, Los Angeles, California 90095-1570; Laboratoire de Chimie Bactérienne, IFR88-CNRS Marseille, France.
4 Molecular Biology Institute.
5 Department of Microbiology, Immunology and Molecular Genetics.