To further probe the conformation of the ssRNA and extend the NMR timescale sensitivity to milliseconds, we measured RDCs (62,63) using 52.4 mg/ml Pf1 phage as an ordering medium. While most RNAs align optimally in $25 mg/ml of phage, a much higher concentration of phage was used for the ssRNA to ensure optimal alignment. To our knowledge, these are the first RDC measurements reported on a single-stranded nucleic acid. The RDCs measured between two nuclei depend on 3 cos 2 À1 2 D E , where is the angle between the inter-nuclear vector and the magnetic field and the angular bracket denotes a timeaverage over all orientations sampled at sub-millisecond timescales (62, 63) . RDCs were measured for base C5H5, C6H6, C8H8, C2H2 and sugar C1 0 H1 0 moieties (47) .