Effect of polynucleotides on the dimerization of glycine

Polynucleotides were found to suppress the dimerization reaction of aqueous glycine with trimetaphosphate as the condensing agent. Small anions (chloride, acetate, and phosphate) did not show this effect. The reaction was studied at a pH of about 11.5 and at 70°C and room temperature with a 13 mM concentration of glycine and trimetaphosphate. Under these conditions, the effect of the polynucleotides was in the following order: polyguanylic acid < polycytidylic acid < polyadenylic acid < polyuridylic acid. The result may have a significant implication for the understanding of processes of chemical evolution.     

Derivatization of unprotected polynucleotides.

A simple and efficient method for attaching amines to the terminal 5'-phosphate of unprotected oligonucleotides or nucleic acids in aqueous solution is described. The method is applicable to low molecular-weight amines, polypeptides, or proteins. The terminal 5'-phosphate of an oligonucleotide or nucleic acid reacts with a water-soluble carbodiimide in imidazole buffer at pH 6 to give good yields of the 5'-phosphorimidazolide. Exposure of the phosphorimidazolide to amine-containing molecules in aqueous solution results in the production of a wide range of stable phosphoramidates in high yield. The exposure of polynucleotides to carbodiimide does not result in significant breakage of phosphodiester bonds or damage to nucleoside bases. The biological activity of a drug resistant plasmid is not affected. The direct condensation of polynucleotides with amines in 1-methylimidazole buffer is also possible. However, it is not a satisfactory preparative method if the ligand is sensitive to carbodiimide.     

Resonance Raman spectroscopy of polynucleotides

Resonance Raman Spectroscopy allows a selective study of the bases of DNA and therefore of the interactions of these bases with ligands. This technique is also sensitive to structural modifications. We show here that, first, the structures of native poly(dA-dT).poly(dA-dT) and poly(dA).poly(dT) are not the same and that, secondly, it is possible to characterize the B----Z transition of poly(dG-dC).poly(dG-dC). The study of the Raman hypochromism during the thermal denaturation of the polynucleotides reveals that the stacking of the adenines in poly(dA).poly(dT) is near that observed in poly(rA) but differs of this stacking in poly(dA-dT).poly(dA-dT). The enhancement of the intensity of the guanine line at 1193 cm-1 and of the cytosine lines at 780 cm-1, 1 242 cm-1 and 1268 cm-1 as well as the shift of the guanine line at low frequency should allow to characterize a small proportion of base pairs in Z form in any DNA.     

Anti-complement activity of polynucleotides.

A biologic assay system, based on complement (C′) inhibition, is described to unravel structural differences among polynucleotides. The C′ system appears particularly suitable to distinguish (1) homo- from copoly-ribonucleotides, (2) deoxyribo- from 2′-OH and other 2′-modified polynucleotides, and (3) single homopolynucleotides from double- or triple-stranded complexes.From these studies a number of polynucleotides emerged with potent anti-C′ activities, worthy of further investigation. The most active polymers were (G)_n (polyguanylic acid), (dCc1)_n [poly(2′-chloro-2′deoxycytidylic acid)] and (dUz)_n [poly(2′-azido-2′-deoxyuridylic acid)].