[Changes in DNA-histone contacts under thermal denaturation of DNP and nucleosomes]

The UV (253.7 nm)-induced binding of the protein to DNA in DNP and nucleosomes at low ionic strength within the temperature range of 5--85 degrees C was studied. A two-step increase in th degree of protein binding was revealed, which was assumed to correspond to two structural conversions in the nucleoproteins during their denaturation. It was shown that the appearance of additional sites of core histone binding in the premelting region is induced by local changes in the DNA structure. None of the four histone fractions was shown to bind preferentially over the whole temperature range studied, which suggests that the structural changes occur all over the length of DNA in the nucleoproteins.