Differential scanning calorimetric and theoretical studies of ColE1 DNA

The differential scanning calorimetry (DSC) of plasmid ColE1 DNA was carried out. The DSC curve under the solvent condition of 1.0 X SSC buffer gave eleven clear peaks over the temperature range of 83 to 98 degrees C. The DSC curves obtained here were essentially in good agreement with the optical melting curves of ColE1 DNA reported previously. The theoretical melting profiles of ColE1 DNA calculated from its entire nucleotide sequence showed a good agreement with the DSC curves. The theoretical analysis made by constructing the thermal stability map showed that there was the positional correlation between the boundaries of the cooperatively melting regions and the ends of the protein coding regions of genes of ColE1. It was shown that the helix-coil transition of many of the small genes had a single cooperatively melting region. However, the large genes such as cea and mob3 had two or more cooperatively melting regions. It was suggested that this is closely related to the domain structures of the proteins encoded by such genes.