S1 Supporting Information Limits of RNA 2ʹ -OH Mimicry by Fluorine: Crystal Structure of Bacillus halodurans RNase H Bound to a 2ʹ F-RNA:DNA Hybrid Pradeep S. Pallan, † Thazha P. Prakash, ‡ Arnie R. de Leon † and Martin Egli* ,† † Department of Biochemistry, Vanderbilt University, Nashville, TN, 37232, USA ‡ Department of Medicinal Chemistry, Ionis Pharmaceuticals Inc., Carlsbad, CA, 92010, USA *Contact: Tel: (615) 343-8070; Fax: (615) 322-7122; E-mail: martin.egli@vanderbilt.edu Table of Contents: BhRNase H expression and purification S2 FRNA and DNA synthesis and purification S2 Crystallization experiments S3 X-ray data collection, structure determination and refinement S3 Data deposition S4 Figure S1: Quality of the final electron density S5 Figure S2: Superimpositions of RNase H complexes with FRNA and RNA S6 Figure S3: Illustrations of helical rise, twist, x-displacement and inclination S7 Table S1: Crystal data, data collection and refinement parameters S8 Table S2: FRNA 2ʹ -F:BhRNase H vs. RNA 2ʹ -OH:BhRNase H contacts S10 Table S3: Curves output for FRNA:DNA duplex A (green) S13 Table S4: Curves output for FRNA:DNA duplex B (blue) S22 Table S5: Curves output for FRNA:DNA duplex C (orange) S31 Table S6: Curves output for RNA:DNA duplex S40 Acknowledgement and References S49