A new approach based on the correlated spectroscopy (COSY) in 2D NMR has been described for determination of sugar geometries in oligonucleotides. Under the usual low resolution conditions employed in COSY, the intensities of cross peaks depend on the magnitudes of coupling constants. There are five vicinal coupling constants in a deoxyribose ring which are sensitive to the sugar geometry. The presence, absence and rough comparison of relative intensities of COSY cross peaks arising from such coupling constants enable one to fix the sugar conformation to a fair degree of precision. The methodology has been applied to d-GAATTCGAATTC.It is observed that ten out of the twelve nucleotide units in this sequence exhibit a rare 01'-endo geometry. The EcoRI cleavage sites (between G and A) in the dodecanucleotide show an interesting variation in the conformation with the two sugars attached to the Gs acquiring a geometry between C2'-endo and C4'-endo. 2D NMR Oligonucleotides solution structure Sugar geometry

A generalization of the half logistic distribution is developed through exponentiation of its cumulative distribution function and termed the Type I Generalized Half Logistic Distribution (GHLD). GHLD's distributional characteristics and parameter estimation using maximum likelihood and modified maximum likelihood methods are presented with comparisons. Comparison of Type I GHLD and the exponential distribution is conducted via likelihood ratio criterion.

No abstract

SynopsisTwo-dimensional (2D) nmr methods (correlated spectroscopy, nuclear Overhauser enhancement spectroscopy, and relayed correlated spectroscopy) have been used to obtain resonance assignment of the nonexchangeable base and sugar protons of a double-helical DNA segment, d-(CG), in D,O solutions under conditions of low ionic strength. Detailed information about the glycosidic torsion angle, sugar geometry, stacking patterns of the bases, and the overall solution structure of the dodecanucleotide has been obtained from the relative intensities of cross-peaks in the 2D spectra. The molecule shows general features of B-DNA under the experimental conditions employed. However, in spite of the repeating base sequence, there are subtle and detectable variations in the structure along the double helix. The terminal residues show considerable conformational flexibility.

No abstract