Monique Monnot

SEQUENCE DEPENDENT EFFECTS OF CPG CYTOSINE METHYLATION : A JOINT 1H-NMR AND 31P-NMR STUDY

The impact of cytosine methylation in the central CpG step of two closely related octanucleotide duplexes d(CATCGATG)2 and d(CTTCGAAG)2 was examined by 1H-NMR and 31P-NMR experiments, and a quantitative structural analysis was performed using the NOE-derived distances, the sugar puckers and the epsilon torsion angles. The two starting oligonucleotides displayed a B-DNA conformation with, however, significant local structure differences. Although the methylated oligonucleotides retained their B-DNA conformation, different structural and thermal stability effects were observed. The magnitude of the methylation effects was to depend on the initial conformation of the CpG site, which is governed by the nature of the dinucleotide AT or TT located on the CpG flanks. As an example of sequence dependence, the methylation of CpG entailed larger conformational variation in d(CATCGATG)2 than in d(CTTCGAAG)2. In this study, the 1H and 31P chemical-shift parameters averred as extremely sensitive probes for detecting subtle conformational changes. Finally, our comparative results may aid our understanding of the structural and related biological effects produced by cytosine methylation in DNA.

A CD study of interactions of ellipticine derivatives with DNA : relations with the in vitro cytotoxicity

UV‐absorption and circular dichroism (CD) experiments showed that ellipticine derivatives may interact with DNA according to 3 possible binding modes depending on their structure and concentration. The first mode concerned intercalation of 1‐methyl‐9‐hydroxyellipticine (1‐Me‐HE) with its long axis perpendicular to the long axis of base pairs. The same drug was able to bind to external sites (second mode) once the intercalation sites were saturated at high concentration. The third mode illustrated by 1,2‐dimethyl‐9‐hydroxyisoellipticinium (1‐Me‐isoNMHE), concerned self‐stacked molecules interacting at the surface of DNA. Biological significance of these different binding modes was then discussed in connection with in vitro cytotoxic activity of compounds.

1H-1H and 13C-13C vicinal coupling constants and amino acid side chain conformation in peptides

Abstract The vicinal coupling constants 13 C′- 13 C γ were measured in aspartic acid and phenylalanine (85 % 13 C enrichment) as free amino acids and in the peptides Asp-Pro and Gly-Pro-Phe. These coupling constants used in connection with those between the α -and the β-protons provide the unambiguous assignment of rotamers I and II in the Asp and Phe side chains. The method is generally applicable to other amino acids and residues even in large peptides. A possible set of J g c,c and J t c,c values is proposed for the use of carbon 13-carbon 13 vicinal coupling constants in the side chain conformational studies of amino acid residues with a free carboxyl group.

31p NMR of a hairpin structure within a 19-Mer DNA

The 31P resonances corresponding to the eighteen phosphate groups of a 19-mer DNA hairpin structure, belonging to a major cleavable site for topoisomerase II were unequivocally assigned and unsual 31P chemical shifts corresponding to those phosphate groups located in the loop were noted.