Biophysical Society Thematic Meeting| Lima 2019

Revisiting the Central Dogma of Molecular Biology at the Single-Molecule Level

Poster Abstracts

12-POS Board 12 NUCLEOSOMAL STATES REGULATES DISASSEMBLY AND ASSEMBLY OF NUCLEOSOMES Cesar D Diaz Celis 1,2 ; Robert Sosa 1 ; Meng Zhang 1 ; Juan Pablo Castillo 1 ; Andy Q Chen 1 ; Bibiana Onoa 1,2 ; Carlos Bustamante 1,2 ; The nucleosome is the structural unit of chromatin and consists of an octamer of histone proteins, wrapped by DNA, which forms ~1.7 turns. Two copies of four histones compose the octamer core: H2A, H2B, H3, and H4. H2A/H2B form a dimer and two dimers of H3/H4 forms a tetramer. Nucleosome dynamics (assembly and disassembly) are fundamental for genomic organization and regulation, and those properties rely on octamer plasticity, DNA sequence, post-translational modifications, regulatory factors, and molecular motors (RNA polymerase, remodelers). We examined the force dependent disassembly of single nucleosomes assembled onto the 601 positioning sequence using single molecule optical trapping. We observed the nucleosome disassemble to form bare DNA in a stochastic manner that generates hexasomes and tetrasomes. Force distribution of the unwrapping of the inner DNA turn indicates that in vitro assembled nucleosomes exists in at least three states characterized by different unwrapping and rewrapping trajectories. The three nucleosomal states were also observed in nucleosomes assembled on the natural 5S positioning sequence, which showed similar unwrapping/rewrapping trajectories and force distributions compared to the 601 sequence. This indicates that nucleosomal states are independent of the DNA sequence and they result from the intrinsic plasticity of the octamer core. These distinct nucleosome states suggest a mechanism that can regulate DNA accessibility to the transcription machinery. 1 University of California, Berkeley, Berkeley, CA, USA 2 Howard Hughes Medical Institute, Berkeley, CA, USA

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