1. Department of Chemistry, University of Manitoba, Winnipeg, MB R3T 2N2, Canada
2. Department of Chemistry and Biochemistry, Alberta RNA Research and Training Institute, University of Lethbridge, Lethbridge, AB T1K 3M4, Canada
3. Department of Biochemistry & Molecular Biology, University of Chicago, Chicago, IL 60637
4. Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637
5. Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada