CORE NUCLEOSOMES BY DIGESTION OF RECONSTRUCTED HISTONE-DNA COMPLEXES

Reconstructed complexes of the inner histories (H2A, H2B, H3, H4) and a variety of DNAs were digested with micrococcal nuclease to yield very homogeneous populations of core nucleosomes (V1). Nucleosomes containing Micrococcus luteus DNA (72% G+C); chicken DNA (43% G+C), Clostridium perfringens DNA (29% G+C); or poly(dA-dT){dot operator}poly(dA-dT) have been examined by circular dichroism, thermal denaturation, electron microscopy, and DNAse I digestion. Circular dichroism spectra of all particles show a typically suppressed ellipticity at 260-280 nm and a prominent α-helix signal at 222 nm. All particles show biphasic melting except v1 (dA-dT), which show three prominent melting transitions at ionic strength ≤1 mM. DNAse I digestion of v1 (dA-dT) produces a ladder of DNA fragments differing in length by one base residue.v1 (dA-dT) contain 146 base pairs of DNA and exhibit an average DNA helix pitch of 10.4-10.5 bases per turn. There appear to be two regions of different DNA pitch within v1 (dA-dT). It is suggested that the two regions of DNA pitch might correspond to the two regions of the melting profiles. © 1979 Information Retrieval Limited.