title: Uranyl photoprobing of nonbent A/T- and bent A-tracts. A difference of flexibility?
abstract: In this study, we have systematically compared the uranyl photocleavage of a range of bent A-tracts and nonbent TA-tracts as well as interrupted A-tracts. We demonstrate that uranyl photocleavage of A-tracts and TA-tracts is almost identical, indicating a very similar minor groove conformation. Furthermore, a 10 base pair A-tract is divided into two independent tracts by an intervening TA or GC step. Uranyl probing also clearly distinguishes the bent A4T4 and the nonbent T4A4 sequences as adopting different structures, and our interpretation of the data is consistent with a structure for the bent A4T4 sequence that resembles a continuous A-tract, whereas the nonbent T4A4 sequences are closer to two independent and opposite A-tracts that cancel each other in terms of macroscopic bending. Finally, we also note that even single TA and TAT steps are highly sensitive to uranyl photocleavage and propose that in addition to average minor groove width, uranyl also senses DNA helix flexibility/deformability. Thus, the structural difference of TA-tracts and A-tracts may to a large extent reflect a difference in flexibility, and DNA curvature may consequently require a rigid narrow minor groove conformation that creates distinct A-tract-B-DNA junctions as the predominant cause of the bending.
authors.affiliation: Department of Medical Biochemistry and Genetics, The Panum Institute, University of Copenhagen Blegdamsvej 3c, 2200 Copenhagen N, Denmark.
authors.forename: Niels Erik
authors.initials: NE
authors.lastname: Møllegaard
authors.forename: Søren
authors.initials: S
authors.lastname: Lindemose
authors.forename: Peter E
authors.initials: PE
authors.lastname: Nielsen
mesh_terms: D020413:3' Untranslated Regions / Q000737:chemistry; D020121:5' Untranslated Regions / Q000737:chemistry; D000225:Adenine / Q000737:chemistry*; D020029:Base Pairing; D004247:DNA / Q000737:chemistry*; D009690:Nucleic Acid Conformation; D009841:Oligonucleotides / Q000737:chemistry; D019920:Photoaffinity Labels / Q000737:chemistry*; D013403:Sugar Phosphates / Q000737:chemistry; D013941:Thymine / Q000737:chemistry*; D014502:Uranyl Nitrate / Q000737:chemistry*
chemical_list: D020413:3' Untranslated Regions; D020121:5' Untranslated Regions; D009841:Oligonucleotides; D019920:Photoaffinity Labels; D013403:Sugar Phosphates; D014502:Uranyl Nitrate; D004247:DNA; D000225:Adenine; D013941:Thymine