1. M. Rep and L. A. Grivell, Section for Molecular Biology, Department of Molecular Cell Biology, University of Amsterdam, Kruislaan 318, 1098 SM Amsterdam, Netherlands.
2. J. M. van Dijl, K. Suda, G. Schatz, C. K. Suzuki, Abteilung Biochemie, Biozentrum der Universität Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland.