title: The role of histone H4 biotinylation in the structure of nucleosomes.
abstract: BACKGROUND
  Post-translational modifications of histones play important roles in regulating nucleosome structure and gene transcription. It has been shown that biotinylation of histone H4 at lysine-12 in histone H4 (K12Bio-H4) is associated with repression of a number of genes. We hypothesized that biotinylation modifies the physical structure of nucleosomes, and that biotin-induced conformational changes contribute to gene silencing associated with histone biotinylation.
  
  
  RESULTS
  To test this hypothesis we used atomic force microscopy to directly analyze structures of nucleosomes formed with biotin-modified and non-modified H4. The analysis of the AFM images revealed a 13% increase in the length of DNA wrapped around the histone core in nucleosomes with biotinylated H4. This statistically significant (p<0.001) difference between native and biotinylated nucleosomes corresponds to adding approximately 20 bp to the classical 147 bp length of nucleosomal DNA.
  
  
  CONCLUSIONS
  The increase in nucleosomal DNA length is predicted to stabilize the association of DNA with histones and therefore to prevent nucleosomes from unwrapping. This provides a mechanistic explanation for the gene silencing associated with K12Bio-H4. The proposed single-molecule AFM approach will be instrumental for studying the effects of various epigenetic modifications of nucleosomes, in addition to biotinylation.
authors.affiliation: Department of Pharmaceutical Sciences, University of Nebraska Medical Center, Omaha, Nebraska, United States of America.
authors.forename: Nina A
authors.initials: NA
authors.lastname: Filenko
authors.forename: Carol
authors.initials: C
authors.lastname: Kolar
authors.forename: John T
authors.initials: JT
authors.lastname: West
authors.forename: S Abbie
authors.initials: SA
authors.lastname: Smith
authors.forename: Yousef I
authors.initials: YI
authors.lastname: Hassan
authors.forename: Gloria E O
authors.initials: GE
authors.lastname: Borgstahl
authors.forename: Janos
authors.initials: J
authors.lastname: Zempleni
authors.forename: Yuri L
authors.initials: YL
authors.lastname: Lyubchenko
mesh_terms: D000818:Animals; D019921:Biotinylation / Q000502:physiology*; D004247:DNA / Q000737:chemistry / Q000378:metabolism; D020868:Gene Silencing; D006657:Histones / Q000378:metabolism*; D018625:Microscopy, Atomic Force; D009690:Nucleic Acid Conformation; D009707:Nucleosomes / Q000378:metabolism / Q000648:ultrastructure*; D011499:Protein Processing, Post-Translational / Q000502:physiology*; D029867:Xenopus Proteins / Q000378:metabolism*
chemical_list: D006657:Histones; D009707:Nucleosomes; D029867:Xenopus Proteins; D004247:DNA