30 research outputs found
Early integration of the individual student in academic activities: a novel classroom concept for graduate education in molecular biophysics and structural biology
Structural plasticity of single chromatin fibers revealed by torsional manipulation
Magnetic tweezers are used to study the mechanical response under torsion of
single nucleosome arrays reconstituted on tandem repeats of 5S positioning
sequences. Regular arrays are extremely resilient and can reversibly
accommodate a large amount of supercoiling without much change in length. This
behavior is quantitatively described by a molecular model of the chromatin 3-D
architecture. In this model, we assume the existence of a dynamic equilibrium
between three conformations of the nucleosome, which are determined by the
crossing status of the entry/exit DNAs (positive, null or negative). Torsional
strain, in displacing that equilibrium, extensively reorganizes the fiber
architecture. The model explains a number of long-standing topological
questions regarding DNA in chromatin, and may provide the ground to better
understand the dynamic binding of most chromatin-associated proteins.Comment: 18 pages, 7 figures, Supplementary information available at
http://www.nature.com/nsmb/journal/v13/n5/suppinfo/nsmb1087_S1.htm
Histone H1 Subtypes Differentially Modulate Chromatin Condensation without Preventing ATP-Dependent Remodeling by SWI/SNF or NURF
Although ubiquitously present in chromatin, the function of the linker histone subtypes is partly unknown and contradictory studies on their properties have been published. To explore whether the various H1 subtypes have a differential role in the organization and dynamics of chromatin we have incorporated all of the somatic human H1 subtypes into minichromosomes and compared their influence on nucleosome spacing, chromatin compaction and ATP-dependent remodeling. H1 subtypes exhibit different affinities for chromatin and different abilities to promote chromatin condensation, as studied with the Atomic Force Microscope. According to this criterion, H1 subtypes can be classified as weak condensers (H1.1 and H1.2), intermediate condensers (H1.3) and strong condensers (H1.0, H1.4, H1.5 and H1x). The variable C-terminal domain is required for nucleosome spacing by H1.4 and is likely responsible for the chromatin condensation properties of the various subtypes, as shown using chimeras between H1.4 and H1.2. In contrast to previous reports with isolated nucleosomes or linear nucleosomal arrays, linker histones at a ratio of one per nucleosome do not preclude remodeling of minichromosomes by yeast SWI/SNF or Drosophila NURF. We hypothesize that the linker histone subtypes are differential organizers of chromatin, rather than general repressors
Conformational Dynamics of the Chromatin Fiber in Solution: Determinants, Mechanisms, and Functions
The structure of the nucleosome core particle of chromatin in chicken erythrocytes visualized by using atomic force microscopy
CENP-A confers a reduction in height on octameric nucleosomes
Nucleosomes in which histone H3 is replaced by CENP-A direct kinetochore assembly. CENP-A nucleosomes extracted from human and Drosophila cells have been reported to have reduced heights relative to canonical octameric H3 nucleosomes, suggesting a unique tetrameric, hemisomal composition. We demonstrate that even octameric CENP-A nucleosomes assembled in vitro exhibit a reduced height, indicating that they are physically distinct from H3 nucleosomes, and negating the need to invoke the presence of hemisomes