1. Sanford-Burnham Medical Research Institute; La Jolla; CA; 92037; USA
2. A. A. Kharkevich Institute for Information Transmission Problems; Russian Academy of Sciences; Moscow; 127994; Russia
3. Department of Chemistry and Biochemistry; University of California San Diego; La Jolla; CA; 92093; USA
4. Department of Molecular and Cell Biology; University of Connecticut; Storrs; CT; 06269; USA