1. Chemistry and Biochemistry Department, and Molecular/Cellular Biology ProgramArizona Stale UniversityTempeArizona85287‐1604USA
2. Institute of Molecular BiologyBulgarian Academy of Sciences1113SofiaBulgaria
3. Biochemistry/Biophysics DepartmentOregon Stale UniversityCorvallisOregon97371‐7305USA
4. Institute of GeneticsBulgarian Academy of Sciences1113SofiaBulgaria