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Biochemistry Seminar: Lu Gan, "Three-dimensional exploration of eukaryotic nuclei"

Lu Gan, Assistant Prof, Dept of Biological Sciences, National University of Singapore, "Three-dimensional exploration of eukaryotic nuclei."
When May 31, 2017
from 12:00 PM to 01:00 PM
Where CUNY ASRC Main Auditorium
Contact Name
Contact Phone 212-650-8803
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ABSTRACT

Chromosome organization at the nucleosome level has long been proposed to influence nuclear activities like transcription, replication, recombination, and chromosome segregation. One of the longstanding textbook models proposes that nucleosomes pack into structures called 30-nm fibers. While there are a number of competing 30-nm-fiber models, they all share common features such as compactness, a high degree of order, and a helical path of sequential nucleosomes. Such fibers are also implied to be highly abundant, explaining the disposition of the majority of nucleosomes in any given cell. We have taken advantage of advances in electron cryotomography (cryo-ET) to explore the life-like organization of chromatin in single-celled eukaryotes such as picoplankton and yeast. We have not found any evidence of 30-nm fibers in cells enriched in interphase or mitosis. Instead, chromatin packing in these cells is better explained by the alternate "liquid" chromatin model, first proposed three decades ago. To our surprise, however, the chromatin from these cells can be induced to form 30-nm fibers when isolated from cells and subjected to a low concentration of divalent cations. The physiological conditions inside cells therefore destabilize the 30-nm fiber.

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