LIFESCI 3 Chapter Notes - Chapter 10.1: Micrococcal Nuclease, Histone Fold, Roger D. Kornberg
Document Summary
10. 1 nucleosomes: the base units of dna condensation. Chromatin: material of chromosomes; protein + dna. Histones: highly conserved basic proteins that assemble into octameric complexes containing two each of four different histone subunits. Dna wraps around histones to form condensed nucleosomes. Chromosomal dna treated with a nonspecific dna nuclease (micrococcal nuclease) Dna cut wherever it"s not associated with proteins. Fragments analyzed for size in a gel. If dna were packaged by proteins into units of a particular size, nuclease would cleave only the dna between these units protected dna segments migrate in gel as a ladder. If there were no regular repeating unit, dna fragments wouldn"t have a regular pattern. Experiments revealed regular spaced dna bands about 200bp apart. Nucleosomes revealed to have four different histone proteins in equimolar ratios. Fifth histone present in about half the amount relative to other four histones. Histones are rich in arginine and lysine (25% of residues)
