[Chromatin structure with no nucleosomes: dissociated SV40 virus]

The mild dissociation of SV40 virus particles at pH 7.5 yields a nucleoprotein complex containing all the capsid proteins and histones of the intact virion. Electron microscopic observations show a bead-on-a-string structure comprising about 70 particles 7 nm in diameter along the viral DNA. No particle of nucleosome size was visible. The compaction of DNA in this complex is lower than 2 and is likely to be close to unity.