1. Institute of Microbiology, Academy of Sciences of the Czech Republic, Vídeňská 1083, 14220 Praha 4, Czech Republic, Department of Biochemistry, Faculty of Science, Charles University, Hlavova 8, 12840 Praha 2, Czech Republic, and Institute of Physics, Faculty of Mathematics and Physics, Charles University, Ke Karlovu 5, 12116 Praha 2, Czech Republic