1. S. Langermann, S. Palaszynski, G. Auguste, J. Burlein, P. Barren, S. Koenig, S. Leath, MedImmune, Inc., Gaithersburg, MD 20878, USA.
2. M. Barnhart, J. S. Pinkner, C. Hal Jones, S. J. Hultgren, Department of Molecular Microbiology, Washington University, St. Louis, MO 63110, USA.