[Nucleoprotein fusion. III. Causes and conditions for development of the multiphase character of the DNA--protein fusion curve].

The influence of proteins reversibly and irreversibly bound to DNA on the shape of melting curve has been considered. It is shown that the melting curve becomes biphasic in two cases: (i) cooperative binding of proteins with DNA (II) STRONG DIFFERENCE IN THE BINDING CONSTANTS WITH HELICAL AND COILED REGIONS. Simple formulae permitting to determine which of two causes stipulate for biphasic profile of a given experimental melting curve are obtained. Melting curves of DNA-basic oligopeptides complexes have been investigated. It is shown that the oligopeptides, when their chain length does not exceed 10, are able to migrate along DNA and biphasic shape of the melting curve is stipulated by the cooperative manner of their binding with DNA.