Sensitivity of non-cooperative binding parameters of ligand-DNA complex by computer analysis.

A simple user-friendly computer programme has been developed to operate on an IBM-PC compatible machine to aid in the process of curve fitting using the McGhee and von Hippel equation [J. Mol Biol, 86 (1974), 469-489] for the analysis of ligand-DNA interactions and the experimental data on berberine-calf thymus DNA and berberine-poly(dI-dC). poly(dI-dC) for non-cooperative binding. A sensitivity analysis on binding constant (K0) and the number of binding sites (N0) show that a small variation in the latter remarkably alters the fitting curve. At a level of 1% change in N0 from the best fit value, the standard deviation grows by almost 4%, while, on the other hand, a 1% change in K0 affects the same value only by less than 0.4%.

Conformational transitions and specific heat anomaly in poly(dG-dC) and its methylated analogue.

The Zimm and Bragg theory of the helix<-->coil transition has been modified to explain order<-->order transitions in polynucleotides, in particular B<-->Z<-->psi(-)<-->coil transitions in poly(dG-dC) and poly(dG-me5dC). Lambda anomalies in specific heat measurements around the transition point have also been explained by a further modification of the same theory. Theoretical results are found to be in good agreement with the experimental data. The nucleation parameter is consistent with the stabilization/destabilization of the ordered states (Z helix) under various environmental conditions, e.g. methylation of cytosine residue at C5 position or change in the cationic concentration of the solvent.