Catasti P, Chen X, Deaven L L, Moyzis R K, Bradbury E M, Gupta G
Theoretical Biology and Biophysics, T-10, MS-K710, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA.
J Mol Biol. 1997 Sep 26;272(3):369-82. doi: 10.1006/jmbi.1997.1248.
Previously, we reported the high resolution NMR structure of the hairpin G-quartet structure formed by the G-rich strand of the insulin minisatellite of repeat sequence, (ACAG4TGTG4/TGTC4ACAC4) located upstream of the human insulin gene. Here, we report structural studies on the C-rich strand of this insulin minisatellite. First, we show by high resolution NMR that (C4TGTC4) forms a hairpin dimer with intercalated C+.C pairs (referred to as the hairpin i-motif); 340 NOE distance constraints uniquely define the nature of hairpin folding and the pattern of C+.C intercalation. Second, we show by one-dimensional NMR spectroscopy and molecular modeling studies that (C4TGTC4ACA4TGTC4) forms an intramolecularly folded hairpin with intercalated C+.C pairs. Third, we demonstrate by in vitro replication studies that several such hairpin i-motifs are present in long (C4TGTC4ACA)n (n>/=6) sequences, even in the presence of their complementary strands. Finally, we discuss structural and biological significance of the hairpin i-motifs formed by the C-rich strands of the insulin minisatellite.
此前，我们报道了位于人类胰岛素基因上游的重复序列胰岛素小卫星富含G链所形成的发夹G-四联体结构的高分辨率核磁共振结构。在此，我们报道对该胰岛素小卫星富含C链的结构研究。首先，我们通过高分辨率核磁共振表明，（C4TGTC4）形成了带有插入C⁺·C对的发夹二聚体（称为发夹i-基序）；340个NOE距离约束唯一地确定了发夹折叠的性质以及C⁺·C插入模式。其次，我们通过一维核磁共振光谱和分子模拟研究表明，（C4TGTC4ACA4TGTC4）形成了带有插入C⁺·C对的分子内折叠发夹。第三，我们通过体外复制研究证明，即使存在其互补链，在长（C4TGTC4ACA）n（n≥6）序列中也存在几个这样的发夹i-基序。最后，我们讨论了胰岛素小卫星富含C链所形成的发夹i-基序的结构和生物学意义。
