Melting curves, denaturation maps, and genetic map of ϕX174: Their relations and applications

In this paper we analyze theoretically the observable details of the differential melting curves (DMC) and the denaturation maps (DM) of a DNA. With the help of a mathematical model, we explore their implications, their relation with each other and with the genetic map of the molecule, and discuss possible future applications. ϕX174 is used as the example, since its sequence and genetic map are available. We find that each gene section of ϕX174 has a characteristic DMC. A reconstruction scheme to get the DMC of a whole piece from those of its constituent genes is shown to be fairly successuful. The relations between the melting curve and the denaturation maps are clarified. We observe that nearly always, the beginning and end of a gene melt at lower temperatures. The sharp features in the DM indicate that despite the long‐range cooperative interactions, the DM do reflect the local sequence effect. Denaturation maps (theoretical) of ϕX174 and SV40 are presented. From available data of other authors, we estimate that the dependence of the melting temperature t m on GC , the fraction of (G+C)‐content, and on x , the ionic concentration in fractions of the standard saline citrate solution, can be expressed as t m ( x , GC ) = ‐5.2 (log x ) GC + 18.4 log x + 41.0 GC + 69.4. The first two coefficients are less certain.