title: Core nucleosomes by digestion of reconstructed histone-DNA complexes.
abstract: Reconstructed complexes of the inner histones (H2A, H2B, H3, H4) and a variety of DNAs were digested with micrococcal nuclease to yield very homogeneous  populations of core nucleosomes (nu 1). Nucleosomes containing Micrococcus luteus DNA (72% G+C); chicken DNA (43% G+C), Clostridium perfringens DNA (29% G+C); or poly(A-dT.poly(dA-dT) have been examined by circular dichroism, thermaldetenaturation, electron microscopy, and DNAse I digestion. Circular dichroism spectra of all particles show a typically suppressed ellipticity at 260--280 nm and a prominent alpha-helix signal at 222 nm. All particles show biphasic melting except nu 1 (dA-dT), which show three prominent melting transitions at ionic strength less than or equal to 1 mM. DNAse I digestion of nu 1 (dA-dT) produces a ladder of DNA fragments fiffering in lengthy by one base residue. nu 1 (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 wihtin nu 1 (dA-dT). It is suggested that the two regions of DNA pitch might correspond to the two regions of the melting profiles.
mesh_terms: D000818:Animals; D002467:Cell Nucleus / Q000032:analysis; D002645:Chickens; D002843:Chromatin / Q000648:ultrastructure*; D002942:Circular Dichroism; D004247:DNA / Q000097:blood; D003851:Deoxyribonucleases; D003852:Deoxyribonucleoproteins / Q000097:blood; D004912:Erythrocytes / Q000032:analysis; D006657:Histones / Q000097:blood; D008836:Micrococcal Nuclease; D009690:Nucleic Acid Conformation; D009691:Nucleic Acid Denaturation; D009698:Nucleoproteins / Q000097:blood; D011067:Poly dA-dT
chemical_list: D002843:Chromatin; D003852:Deoxyribonucleoproteins; D006657:Histones; D009698:Nucleoproteins; D011067:Poly dA-dT; D004247:DNA; D003851:Deoxyribonucleases; D008836:Micrococcal Nuclease