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H T Miles

Publications and source records attributed to H T Miles.

At least 55 records · Page 3Linked to original sources
PubMed1983

A thermally driven interconversion of B and Z-dna.

CD and IR studies show that poly(dG-dMeC) in dilute Mg++ and Na+ solutions (e.g., 2 mM Mg++ and 55 mM Na+) undergoes reversible thermal interconversion of B and Z forms, in contrast to previous reports that the transition is independent of temperature and has an enthalpy change of zero. The B conformation is stable under the above conditions at lower temperature (approximately 5 degrees) and the Z form above approximately 20 degrees. The conversion is relatively slow in both directions, but is more rapid in the Z leads to B direction.

Circular Dichroism↗
PubMed1983

Poly(8-methyladenylic acid): a single-stranded regular structure with alternating syn-anti conformations.

Poly(8-methyladenylic acid) has been prepared by chemical synthesis of 8-methyladenosine 5'-diphosphate and enzymatic polymerization with polynucleotide phosphorylase. The polymer exhibits a large hypochromism and cooperative melting in neutral solution. The transition temperature is independent of salt concentration at moderate ionic strength and decreases slightly at high salt. The adenine ring vibration at 1626 cm-1 is independent of temperature. A high-resolution nuclear magnetic resonance spectrum is observed near the bottom of the melting range. The chemical shift of the H2 proton exhibits a large upfield shift in the ordered form, and the temperature profile of H2 is cooperative and congruent with the UV melting curve. The CH3 proton signal, in striking contrast to H2, is independent of temperature. These results support a regular, single-stranded helix in the ordered form, in contrast to both poly(adenylic acid) and poly(8-bromoadenylic acid). We suggest that the contrasting temperature dependence of the H2 and CH3 proton signals can be accounted for by regularly alternating syn and anti conformations of the 8-methyladenylic acid residues.

Magnetic Resonance Spectroscopy↗
PubMed1982

Binding isotherms of nucleosides and polynucleotides measured by continuous ultrafiltration at constant volume: a rapid and precise technique.

Equilibrium binding isotherms have been measured as a function of temperature for the interaction of 2- and 8-aminoadenosine with poly(U) by continuous, constant-volume ultrafiltration. An analytical method is described for determining the entire isotherm in a single experiment on a preequilibrated ligand--polymer solution. The method is shown to produce the same results as classical equilibrium dialysis but to be much more rapid and convenient. Values of the enthalpy, equilibrium constant, and free energy of stacking as a function of temperature are derived from the binding data. Stoichiometry of interaction is obtained from the diafiltration profiles as well as from the binding isotherms. Over the temperature range studied, the cooperativity of binding is observed to increase with rising temperature.

Adenosine↗
PubMed1980

Copolymers of adenylic and 2-aminoadenylic acids. Effect of progressive changes in hydrogen bonding and stacking on interaction with poly(uridylic acid).

Random copolymers of adenylic acid and 2-aminoadenylic acid form both double and triple helices with poly(uridylic acid) [poly(U)]. Transition temperatures of two-stranded helices increase with 2NH2A content, exhibiting a slight positive departure from linearity and indicating that the contribution to helix stability arising from introduction of the 2-amino group does not significantly depend upon base sequence. We have shown previously that poly(2NH2A) . poly(U) does not undergo a disproportionation reaction (2 leads to 3 transition). Extrapolation from melting curves of 1:1 complexes between A,2NH2A copolymers and poly(U) indicates a Tm for the 2 leads to 3 transition of poly(2NH2A) . poly(U) which is too high to be observable under normal conditions. Addition of an organic solvent (50% ethylene glycol), however, lowers Tm by promoting unstacking of single-stranded poly(2NH2A) sufficiently to permit observation of the disproportionation of poly(2NH2A) . poly(U) for the first time. Transition breadths of 1:1 complexes of A,2NH2A copolymers with poly(U) are greater than those of either of the homopolymer complexes in the middle range of composition (67 and 48% A) but not at 25% A. These results are consistent with previous calculations on the effect of heterogeneity in base-pair stability on DNA transition breadths. In the poly(A), poly(U) system, Et4N+ counterion reduces the Tm of the double and triple helices by 26 and 41 degrees C, respectively. The larger depression in the latter case arises from the higher charge density of the triple helix and less effective counterion screening by Et4N+. In the poly(2NH2A), poly(U) system Tm,2 leads to 1 is reduced by 24 degrees C, but extrapolation of the copolymer results indicates a reduction of approximately 100 degrees C for Tm,3 leads to 2, accounting for previous failure to observe a triple helix in this system. CD spectra of A,2NH2A copolymers suggest that much of the spectral region can be regarded as a contribution of the CD spectra of the parent polymers poly(A) and poly(2NH2A) but that the region from 255 to 275 nm requires that contributions made by longer range interactions be taken into account.

Circular Dichroism↗
PubMed1978

Infrared spectroscopy of polynucleotides in the carbonyl region in H2O solution: A.U systems.

Strong absorbance of water at 1645 cm-1 has previously prevented dependable observation of infrared spectra of H2O solutions in the carbonyl region. We have obtained reliable spectra in pure water and in alcohol-water mixtures in this region and used them to study A.U polynucleotide interaction. Spectra in pure water were obtained by computer subtraction of solvent from that of solution measured in short path length cells. Mixed solvents, by diluting the water, permit use of longer cells and standard double-beam compensation methods. Poly(adenylic acid) in H20 solution has a strong NH2 deformation band at 1659 cm-1 coupled to an A ring vibration at 1605 cm-1. Poly(uridylic acid) has a broad band at approximately 1695 cm-1, predominantly C2 carbonyl stretch, an unresolved CR carbonyl band (probably near 1660 cm-1), and a ring vibration at approximately 1636 cm-1. The large changes these spectra undergo when helical structures are formed are discussed and compared with changes observed in D2O.

Adenosine Monophosphate↗
PubMed1977

Structure of poly 8-bromoadenylic acid; conformational studies by CPF energy calculations.

Poly 8-bromoadenylic acid [poly(BBrA)] is the only known all-syn polynucleotide. It shows a helix-coil transition with a melting curve centred around 55 degrees C. Energy calculations based on classical potential functions have been used to explore the three-dimensional structure of this polymer in helix and random coil. It is concluded that the ordered state is a helix of two parallel strands with a two-fold rotation axis, and the duplex is stabilised by hydrogen bonds involving N1 and H6. Each strand has a conformation with C3' endo geometry, phi' = 216 degrees, omega' = 280 degrees, omega = 294 degrees, phi = 179 degrees, chi = 243 degrees and psi = 57 degrees. Such a conformation leads to approximately 8 nucleotide units per turn of the helix and an axial rise of 3.9A degrees. The structure of poly(8BrA) has been compared with that of the related polymer poly(A) which forms a double helical structure in acidic conditions with bases in the anti conformation and with interstrand hydrogen-bonds between N7 and H6. This is the first time that a specific geometrical model of a novel polynucleotide structure has been produced initially by potential energy calculations, though such calculations on a number of known structures have been reported previously.

Models, Molecular↗
PubMed1976

Poly(2-aminoadenylic acid): interaction with poly(uridylic acid).

Poly(2-aminoadenylic acid) forms both double and triple helices with poly(uridylic acid) [poly(U)]. The 2-amino group forms a third hydrogen bond, elevating the 2 leads to 1 transition temperature by 33 degrees C. The third strand, however, has about the same stability as poly(A)-2poly(U), as measured by Tm 3 leads to 2. This selective stabilization of the two-stranded helix results in a much greater resolution of the differnt thermal transitions than that observed in analogous polynucleotide systems. In contrast to other A, U systems 3 leads to 1 and 2 leads to 3 transitions are not observed under any conditions, and the triple helix always undergoes a 3 leads to 2 transition even at very high ionic strength. A 1:1 mixture of poly(2NH2A) and poly(U) exhibits no transient formation of 1:2 complex, unlike similar mixtures of poly(A) with poly(U) and poly(T). This difference is evidently due to a more rapid displacement reaction: [poly(2NH2A) + poly(2NH2A)-2poly(U) leads to 2 poly(2NH2A)-poly(U)] With poly(2NH2A) than with poly(A). We describe a method for establishing the combining ratios of polynucleotide complexes which used a computer to calculate the angles of intersection of mixing curves as explicit and continuous functions of the wavelength. The wavelength dispersions of the angles of intersection determine optimum wavelengths for establishing stoichiometry and can also provide reliable negative evidence that presumably plausible complexes are not formed. Analogous computer procedures have been developed to determine wavelengths which are selective for the formation of both 1:1 and 1:2 complexes. Infrared spectra of the 1:1 and 1:2 complexes resemble those of other A, U homoribopolynucleotide helices in having two and three strong bands, respectively, in the region of carbonyl stretching vibrations. CD spectra of the two complexes are unusual in having negative first extrema of moderate intensity. We attribute these extrema to intrastrand interactions of strong, well-resolved transitions at 278 nm (B2u) of the 2-aminoadenine residues. The CD spectra are correlated with those of other polynucleotide helices.

Autoanalysis↗
PubMed1975

Poly(8-aminoguanylic acid): formation of ordered self-structures and interaction with poly(cytidylic acid).

Poly(8-aminoguanylic acid) has in neutral solution a novel ordered structure of high stability. The 8-amino group permits formation of three hydrogen bonds between two residues along the "top", or long axis, of the purines. The usual hydrogen bonding protons and Watson-Crick pairing sites are not involved in the association. The bonding scheme has a twofold rotation axis and is hemiprotonated at N(7). Poly(8NH2G) is converted by alkaline titration (pK = 9.7) to a quite different ordered structure, which is the favored form over the range approximately pH 10-11. The bonding scheme appears to be composed of a planar, tetrameric array of guanine residues, in which the 8-amino group does not participate in interbase hydrogen bonding. Poly (8NH2G) does not interact with poly(C) in neutral solution because of the high stability of the hemiprotonated G-G self-structure. Titration to the alkaline plateau, however, permits ready formation of a two-stranded Watson-Crick helix. In contrast to the monomer 8NH2GMP, poly(8NH2G) does not form a triple helix with poly(C) under any conditions. The properties of the ordered structures are interpreted in terms of a strong tendency of the 8-amino group to form a third interbase hydrogen bond, when this possibility is not prevented by high pH.

Binding Sites↗
PubMed1975

Poly(8-bromoadenylic acid): synthesis and characterization of an all-syn polynucleotide.

Poly(8-bromoadenylic acid) (poly(8-BrA)) has been synthesized by polymerization of 8-BrADP with polynucleotide phosphorylase in the presence of oligonucleotide primers. In the absence of oligonucleotides, significant (i.e. more than 1%) polymerization does not occur. Oligo(I) primer was removed selectively from the polymer with ribonuclease T1 to yield the homopolymer, poly(8-BrA). End group analysis, based on quantitative infrared measurement of the (Ip)3I-primed polymer, indicates an average degree of polymerization of about 70 residues. The primed polymers and the homopolymer appear to have similar helical structures, probably double-stranded with mutual hydrogen bonding interaction of BrA residues. Preliminary NMR observations of poly(8-BrA) with a tetrainosinic acid primer at the 5' ends of the polymer chain ((Ip)3I-(8-BrA)n) are consistent with the existence of a rigid helical structure below the melting range of the primed polymer. Above the melting range (81 degrees) the H1' coupling constants of (Ip)3I-(8-BrA)n and of polyadenylic acid (poly(A)) suggest a significantly higher population of C3' endo conformation of ribose residues in the primed polymer than in poly(A) at 81 degrees.

Adenosine Monophosphate↗