Circular dichroism of native whole SV40 chromatin.

Circular dichroism properties of SV40 virions, isolated minichromosomes from virions, and SV40 Form I (supercoiled) DNA were studied in a buffer of low ionic strength. The isolated minichromosomes are compact as judged by sedimentation and electron microscopy. The molar ellipticity at 284 nm of the virion, which may be regarded as a minichromosome in its native state, is about 1500 deg cm²/dmol phosphate; this value is in the same range as that reported for core particles (1300–2000) isolated from different sources. When the viral capsid is removed, there is a small increase in the molar ellipticity to about 2000. However, both of these values are much lower than that found for SV40 supercoiled DNA (about 8200). The results strongly suggest that the linker DNA of the native whole chromatin contributes in a similar fashion to the circular dichroic ellipticity as the core DNA.