title: Monitoring RNA base structure and dynamics using site-directed spin labeling.
abstract: Site-directed spin labeling utilizes site-specific attachment of a stable nitroxide radical to probe the structure and dynamics of macromolecules. In the present study, a 4-thiouridine base is introduced at each of six different positions in a 23-nucleotide RNA molecule. The 4-thiouridine derivatives were subsequently modified with one of three methanethiosulfonate nitroxide reagents to introduce a spin label at specific sites. The electron paramagnetic resonance spectra of the labeled RNAs were analyzed in terms of nitroxide motion and the RNA solution structure. At a base-paired site in the RNA helix, where the nitroxide has weak or no local interactions, motion of the nitroxide is apparently dominated by rotation about bonds within the probe. The motion is similar to that found for a structurally related probe on helical sites in proteins, suggesting a similar mode of motion. At other sites that are hydrogen bonded and stacked within the helix, local interactions within the RNA molecule modulate the nitroxide motion in a manner consistent with expectations based on the known structure. For a base that is not structurally constrained, the mobility is higher than at any other site, presumably due to motion of the base itself. These results demonstrate the general utility of the 4-thiouridine/methanethiosulfonate coupling method to introduce nitroxide spin labels into RNA and the ability of the resulting label to probe local structure and dynamics.
authors.affiliation: Jules Stein Eye Institute and Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095, USA.
authors.forename: Peter Z
authors.initials: PZ
authors.lastname: Qin
authors.forename: Kálmán
authors.initials: K
authors.lastname: Hideg
authors.forename: Juli
authors.initials: J
authors.lastname: Feigon
authors.forename: Wayne L
authors.initials: WL
authors.lastname: Hubbell
mesh_terms: D001483:Base Sequence; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D009589:Nitrogen Oxides / Q000032:analysis / Q000737:chemistry*; D009690:Nucleic Acid Conformation; D012313:RNA / Q000737:chemistry* / Q000235:genetics; D013113:Spin Labels; D013816:Thermodynamics; D013891:Thiouridine / Q000031:analogs & derivatives*
chemical_list: D009589:Nitrogen Oxides; D013113:Spin Labels; D013891:Thiouridine; D012313:RNA; C039900:nitroxyl