1. J. Pettersson, R. Nordfelth, E. Dubinina, T. Berman, H. Wolf-Watz, Department of Cell and Molecular Biology, University of Umeå, S-901 87 Umeå, Sweden.
2. M. Gustafsson and K. E. Magnusson, Department of Medical Microbiology, University of Linköping, S-581 85 Linköping, Sweden.