Circular dichroism of native and reconstituted nucleohistones

Circular dichroism (CD) spectra of histone, DNA and native, partial and reconstituted nucleohistone complexes in 0.01 M Tris buffer in which nucleohistone complexes appear to be intact and in 2 M NaCl, in which complexes are mostly dissociated, have been compared. The CD spectra in the longwave region, where the protein contribution is negigible, reveal differences in the spectra for DNA in nucleohistone complexes as compared with that of free DNA, the difference being roughly proportional to the protein DNA ratio. An analysis of the shape of the first positive CD maximum suggests that we are probably dealing here with slight conformational changes on DNA. Minor differences between the behavior of native and reconstituted complexes may be due to the effect of different conformational states of the protein component.