Rat liver HMG1: a physiological nucleosome assembly factor.
Incubation of rat liver single-stranded DNA-binding protein HMG1 with the four core histones at 0.15 M NaCl favors histone association primarily into tetramers and, to a lesser extent, into octamers. The assembly of pre-formed histone-HMG1 complexes with DNA yields nucleosome-like subunits which satisfy most of the criteria defining native core particles: (i) the circular DNA extracted from the complexes is supercoiled indicating that the initially relaxed DNA acquired superhelical turns during complex formation in the presence of topoisomerase I; (ii) the digestion of the complexes with micrococcal nuclease yields a DNA fragment of approximately 140 bp in length; (iii) electron microscopy of the reconstituted complexes shows a beaded structure with the DNA wrapped around the histone cores, leading to a reduction in the contour length of the genome compared with free DNA. Moreover, in the presence of HMG1, nucleosome assembly occurs rapidly at 0.15 M NaCl. Therefore, in addition to its DNA-binding properties, HMG1 mediates the assembly of nucleosomes in vitro under conditions of physiological ionic strength. The possible involvement of these properties in the DNA replication process is discussed.
D000818:Animals; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism*; D004264:DNA Topoisomerases, Type I / Q000378:metabolism; D004277:DNA, Single-Stranded / Q000378:metabolism; D004120:Dimethyl Suberimidate; D006609:High Mobility Group Proteins; D006657:Histones / Q000378:metabolism*; D008099:Liver / Q000502:physiology*; D008836:Micrococcal Nuclease; D008854:Microscopy, Electron; D009707:Nucleosomes / Q000502:physiology*; D011485:Protein Binding; D051381:Rats
D002868:Chromosomal Proteins, Non-Histone; D004277:DNA, Single-Stranded; D006609:High Mobility Group Proteins; D006657:Histones; D009707:Nucleosomes; D004120:Dimethyl Suberimidate; D008836:Micrococcal Nuclease; D004264:DNA Topoisomerases, Type I