Influence of DNA acidification on DNA premelting and template properties

Acidification of a T7 DNA sample was found to be partly irreversible as ultraviolet difference spectra measured at various sub-melting temperatures were different from those observed for a 'normal' DNA sample. This implies some subtle conformational change which is not reversed by return to neutral pH. In the same conditions, only poly(purine)-poly(pyrimidine) polymers behaved in a different manner, during premelting, according to whether they were previously acidified or not. The properties of acidified and reneutralized T7 DNA were also investigated for Escherichia coli RNA polymerase binding and transcription. An inhibition of RNA synthesis and chain initiation was observed. The results suggest that the binding of the enzyme is affected. RNA synthesized is specific but there is a decrease in the number and in the stability of the RNA-polymerase-DNA complexes.