Denaturation maps of DNA: experimental and theoretical maps of phiX174 DNA.

A formaldehyde denaturation map of the replicative form of phiX174 DNA is obtained. The RFI DNA was converted into a linear state by restriction endonuclease pst I which introduces into this DNA a single double-stranded break. The map has four clear-cut peaks. Their positions excellently correlate with the peak positions on the map of equilibrium denaturation theoretically obtained earlier from the known nucleotide sequence of phiX174 DNA. The sequence is also used for a calculation of the maps of smoothed AT-content. The maxima on these maps correlate well with the peaks on the denaturation maps. To reveal the causes of a good correlation between the experimental formaldehyde and theoretical equilibrium denaturation maps, the theoretical formaldehyde denaturation maps are calculated for different conditions (temperature, formaldehyde concentration) using the detailed theory of DNA interaction with formaldehyde developed earlier.