Showing papers by "Eric Henderson published in 1994"
TL;DR: The results described here extend the understanding of the structural potential of G-rich nucleic acids and may provide insight into the possible roles ofG-rich sequences and the novel structures they can form in biological systems.
Abstract: The telomeric DNA oligonucleotide 5'-G4T2G4-3' (Tet 1.5) spontaneously assembles into large superstructures we have termed G-wires. G-wires can be resolved by gel electrophoresis as a ladder pattern. The self-association of Tet 1.5 is noncovalent and exhibits characteristics of G4-DNA, a parallel four-stranded structure stabilized by guanine tetrads. Formation of G-wires is dependent upon the presence of Na+ and/or K+, and once formed, G-wires are resistant to denaturation. The results described here extend our understanding of the structural potential of G-rich nucleic acids and may provide insight into the possible roles of G-rich sequences and the novel structures they can form in biological systems.
142 citations
TL;DR: Calcium channels were in low and high density areas and exhibited a prominent interchannel spacing of 40 nm, indicating an intermolecular linkage, and particles were observed in clusters and short linear or parallel linear arrays, groupings that may reflect calcium channel organization at the transmitter release site.
116 citations
TL;DR: The atomic force microscope (AFM) as discussed by the authors generates images of samples by measuring force interactions between the sample and a small, sharp tip on the end of a flexible cantilever.
115 citations
TL;DR: Oligonucleotides composed of 2 or 4 repeats of the human telomeric C–strand sequence d(CCCTAA)n are examined, suggesting that four contiguous cytosine tracts fold into a C·C+ intercalated tetraplex.
Abstract: Telomeric C-strand sequences form non-Watson-Crick base-paired structures in supercoiled plasmids and in oligonucleotides at low pH. Here we examine oligonucleotides composed of 2 or 4 repeats of the human telomeric C-strand sequence d(CCCTAA)n. At low pH, the 2-repeat molecule forms a dimer which exhibits H1'-H1' nuclear Overhauser effects (NOEs) between stacked CC+ base pairs. These NOEs are characteristic of the i-motif, which is a tetraplex composed of two intercalated CC+ duplexes. The 4-repeat molecule forms an intramolecular monomeric structure at low pH, suggesting that four contiguous cytosine tracts fold into a CC+ intercalated tetraplex. These unusual structures may be relevant to the formation of guanine tetraplexes by complementary G-rich sequences. They may also provide a general mechanism for self-recognition by nucleic acids.
101 citations
TL;DR: In this article, the authors used colloidal gold particles as hard, spherical imaging targets to assist in the 3D reconstruction of the atomic force probe apex, which was shown to be accurate to 1 nm resolution and dynamically change as the sample is scanned.
Abstract: Colloidal gold particles are used as hard, spherical imaging targets to assist in the three‐dimensional reconstruction of the atomic force probe apex. Probe reconstructions are shown to be accurate to 1 nm resolution and dynamically change as the sample is scanned, emphasizing the utility of colloidal gold particles as in situ calibration standards for image reconstruction of a coadsorbed specimen.
79 citations
TL;DR: During the course of this study, it was determined that Mg2+ facilitates the formation of parallel-stranded G4-DNA structures and that high oligonucleotide concentrations are not required to drive formation of these structures.
Abstract: G4-DNA is a parallel, four-stranded structure mediated by tetrads of hydrogen-bonded guanines (G-quartets). An abundant protein called Tetrahymena G4 binding protein (TGP) that binds to an intermolecular, quadruplex form of d(TTGGGGTTGGGGTTGGGGTTGGGG) under physiological salt conditions has been identified in cellular extracts from the ciliated protozoan Tetrahymena thermophila. In binding competition experiments, molecules capable of forming G4 structures compete for binding to TGP, but non-G4-forming molecules and r(U2G4)4 do not. TGP binding also requires a single-stranded region adjacent to the G4 structure. During the course of this study, it was determined that Mg2+ facilitates the formation of parallel-stranded G4-DNA structures and that high oligonucleotide concentrations are not required to drive formation of these structures. In addition, G4-DNA and TGP/G4-DNA complexes form readily under physiological salt conditions. These data support the proposal that G4-DNA structures exist in vivo.
61 citations
TL;DR: Topographic evolution during passivation was very similar for pits as for tunnels, except that the time scale of the process is much longer for tunnels than for pits (200--300 ms vs. 11--20 ms).
Abstract: The time evolution of microscopic topography on corroding aluminum surfaces during oxide film passivation was characterized. Passivation was studied after galvanostatic etching in 1N HCl at 65 C, in both aluminum etch tunnels (by scanning electron microscopy) and micron-size cubic etch pits (by atomic force microscopy). Step reductions of applied current initiated passivation. At times of 1 to 300 ms after current steps, the corroding surface was microscopically heterogeneous, consisting of a number of small corroding patches 0.1 to 1 [mu]m in width, which were surrounding by passive surface. As some patches grew by dissolution, others were passivated, until eventually only one patch remained on the pit or tunnel surface. The topography of the corroding surface was controlled by the potential: the surface dissolved uniformly at the repassivation potential E[sub R], while partial passivation to produce patches occurred at potentials more cathodic than E[sub R]. Patches were unstable at potentials below E[sub R] and would ultimately passivate. Topographic evolution during passivation was very similar for pits as for tunnels, except that the time scale of the process is much longer for tunnels than for pits (200--300 ms vs. 11--20 ms). The difference of time scales was due to the differentmore » corroding surface areas of pits and tunnels. Patches are probably defined by a surface layer which inhibits passivation.« less
16 citations
Journal Article•
6 citations
DOI•
03 Jun 1994
TL;DR: Three examples of the application of AFM to the study of biological questions are provided, including the localization of calcium channels on the release face of a nerve terminal and analyses of a new form of DNA, the G-wire.
Abstract: The atomic force microscope (AFM) is proving to be a powerful tool for analysis of biological samples. We provide three examples of the application of AFM to the study of biological questions. First, polytene chromosomes from Drosophila are imaged and manipulated by the AFM. Second, the localization of calcium channels on the release face of a nerve terminal is described. Finally, analyses of a new form of DNA, the G-wire, is presented. These examples illustrate the wide variety of biological questions to which AFM can contribute.