title: Photobleaching studies reveal that a single amino acid polymorphism is responsible for the differential binding affinities of linker histone subtypes H1.1 and H1.5.
abstract: Mammals express six major somatic linker histone subtypes, all of which display dynamic binding to chromatin, characterized by transient binding at a given location followed by rapid translocation to a new site. Using photobleaching techniques, we systematically measured the exchange rate of all six mouse H1 subtypes to determine their relative chromatin-binding affinity. Two subtypes, H1.1 and H1.2, display binding affinities that are significantly lower than all other subtypes. Using in vitro mutagenesis, the differences in chromatin-binding affinities between H1.1 (lower binding affinity) and H1.5 (higher binding affinity) were mapped to a single amino acid polymorphism near the junction of the globular and C-terminal domains. Overexpression of H1.5 in density arrested fibroblasts did not affect cell cycle progression after release. By contrast, overexpression of H1.1 resulted in a more rapid progression through G1/S relative to control cells. These results provide structural insights into the proposed functional significance of linker histone heterogeneity.
authors.affiliation: Department of Biochemistry, University of Mississippi Medical Center, Jackson, MS 39216, USA.
authors.forename: Thomas W
authors.initials: TW
authors.lastname: Flanagan
authors.affiliation: Clinton High School, Clinton, MS 39056, USA Spring Hill College, Mobile, AL 36608, USA.
authors.forename: Jacob K
authors.initials: JK
authors.lastname: Files
authors.affiliation: Saint Andrew's Episcopal School, Ridgeland, MS 39157, USA.
authors.forename: Kelsey Rose
authors.initials: KR
authors.lastname: Casano
authors.affiliation: Department of Biochemistry, University of Mississippi Medical Center, Jackson, MS 39216, USA Department of Physiology, University of Mississippi Medical Center, Jackson, MS 39216, USA.
authors.forename: Eric M
authors.initials: EM
authors.lastname: George
authors.affiliation: Department of Biochemistry, University of Mississippi Medical Center, Jackson, MS 39216, USA dbrown@umc.edu.
authors.forename: David T
authors.initials: DT
authors.lastname: Brown
keywords: Chromatin; FRAP; Histone H1; Linker histone