Poster abstracts
Poster number 4 submitted by Nathaniel Burge
The effect of histone H1 chaperones on H1 dynamics and nucleosomal DNA accessibility.
Nathaniel Burge (OSBP), Jenna Thuma (Physics), Michael Poirier (Physics)
Abstract:
Histone H1 is responsible for compaction of chromatin into higher order structures. H1 binding to nucleosomes reduces accessibility of DNA to transcription factors (TF) and other proteins by reducing DNA unwrapping from the histone octamer core. This is one mechanism by which H1 regulates transcription activation. Separately, H1 is regulated by the chaperones, somatic nuclear autoantigenic sperm protein (sNASP) and nucleosome assembly protein 1 (Nap1), which transport H1 into the nucleus and deposit it onto chromatin. The influence of chaperones on H1-nucleosome occupancy, nucleosome dynamics, and TF binding is not well understood, but is important to fully understand the regulation of transcription activation. To monitor H1 dynamics and regulation of TF binding in mononucleosomes, we utilized native gel electrophoresis and ensemble FRET measurements between fluorophores attached to DNA, the histone octamer, and H1. The binding affinity of the TF Gal4 to nucleosomes was reduced 4-fold when H1 was bound to the nucleosomes. At high enough concentrations, sNASP and Nap1 appear to be able to remove H1 from nucleosomes. Preliminary data shows when the two chaperones were added at concentrations high enough to remove H1, the binding affinity of Gal4 remained decreased by 4-fold as if H1 still remained bound to the nucleosomes. Further characterization of these events is clearly needed and are ongoing. In addition to measuring the effect of H1 on TF binding, we monitored FRET between different parts of the nucleosome and H1 when a TF binds to determine H1 dynamics during TF binding. Our data suggests H1 remains bound to the nucleosome dyad while a nucleosome unwraps during TF binding. These initial studies provide insight into the role of histone H1 chaperones on regulating TF binding and the dynamics of H1 when a TF binds to a nucleosome.
Keywords: Histone H1, Histone Chaperones, Transcription