1. Division of Radiation and Molecular Biophysics, B. P. Konstantinov Institute of Nuclear Physics of the Russian Academy of Sciences, Gatchina, St. Petersburg 188350, Russia
2. Department of Mathematics no. 2, St. Petersburg Electro-Technical Institute, 5 Popova, St. Petersburg, Russia
3. Laboratory of Ribosomal Structure and Function, Institute of Bioorganic Chemistry, Siberian Division of the Russian Academy of Sciences, Novosibirsk, Russia