title: NMR structure of stem-loop SL2 of the HIV-1 psi RNA packaging signal reveals a novel A-U-A base-triple platform.
abstract: The genome of the human immunodeficiency virus type-1 (HIV-1) contains a stretch of approximately 120 nucleotides known as the psi-site that is essential for RNA packaging during virus assembly. These nucleotides have been proposed to form four stem-loops (SL1-SL4) that have both independent and overlapping functions. Stem-loop SL2 is important for efficient recognition and packaging of the full-length, unspliced viral genome, and also contains the major splice-donor site (SD) for mRNA splicing. We have determined the structure of the 19-residue SL2 oligoribonucleotide by heteronuclear NMR methods. The structure is generally consistent with the most recent of two earlier secondary structure predictions, with residues G1-G2-C3-G4 and C6-U7 forming standard Watson Crick base-pairs with self-complementary residues C16-G17-C18-C19 and A12-G13, respectively. However, residue A15, which is located near the center of the stem, does not form a predicted bulge, and residues A5 and U14 do not form an expected Watson-Crick base-pair. Instead, these residues form a novel A5-U14-A15 base-triple that appears to be stabilized by hydrogen bonds from A15-H61 and -H62 to A5-N1 and U14-O2, respectively; from A5-H61 to U14-O2, and from C16-H42 to U14-O2'. A kink in the backbone allows the aromatic rings of the sequential U14-A15 residues to be approximately co-planar, adopting a stable "platform motif" that is structurally similar to the A-A (adenosine) platforms observed in the P4-P6 ribozyme domain of the Tetrahymena group I intron. Platform motifs generally function in RNA by mediating long-range interactions, and it is therefore possible that the A-U-A base-triple platform mediates long-range interactions that either stabilize the psi-RNA or facilitate splicing and/or packaging. Residue G8 of the G8-G9-U10-G11 tetraloop is stacked above the U7-A12 base-pair, and the remaining tetraloop residues are disordered and available for potential interactions with either other RNA or protein components.
authors.affiliation: Howard Hughes Medical Institute, University of Maryland, Baltimore County 21250, USA.
authors.forename: G K
authors.initials: GK
authors.lastname: Amarasinghe
authors.forename: R N
authors.initials: RN
authors.lastname: De Guzman
authors.forename: R B
authors.initials: RB
authors.lastname: Turner
authors.forename: M F
authors.initials: MF
authors.lastname: Summers
mesh_terms: D000818:Animals; D020029:Base Pairing / Q000235:genetics; D001483:Base Sequence; D015497:HIV-1 / Q000235:genetics*; D006860:Hydrogen Bonding; D007438:Introns / Q000235:genetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D008970:Molecular Weight; D019906:Nuclear Magnetic Resonance, Biomolecular; D009690:Nucleic Acid Conformation; D009843:Oligoribonucleotides / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D011522:Protons; D020871:RNA Stability; D012367:RNA, Viral / Q000737:chemistry* / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D013768:Tetrahymena / Q000235:genetics; D013816:Thermodynamics; D019065:Virus Assembly / Q000235:genetics*
chemical_list: D009843:Oligoribonucleotides; D011522:Protons; D012367:RNA, Viral