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Updated: Aug 22, 2025

Bacterial Artificial Chromosomes: A Functional Genomics Tool for the Study of Positive-strand RNA Viruses
Published on: December 29, 2015
A giant virus genome is densely packaged by stable nucleosomes within virions
Terri D Bryson1, Pablo De Ioannes2, Marco Igor Valencia-Sánchez2
1Basic Sciences Division, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA; Howard Hughes Medical Institute, Chevy Chase, MD, USA.
Abstract:
The two doublet histones of Marseillevirus are distantly related to the four eukaryotic core histones and wrap 121 base pairs of DNA to form remarkably similar nucleosomes. By permeabilizing Marseillevirus virions and performing genome-wide nuclease digestion, chemical cleavage, and mass spectrometry assays, we find that the higher-order organization of Marseillevirus chromatin fundamentally differs from that of eukaryotes. Marseillevirus nucleosomes fully protect DNA within virions as closely abutted 121-bp DNA-wrapped cores without linker DNA or phasing along genes. Likewise, we observed that nucleosomes reconstituted onto multi-copy tandem repeats of a nucleosome-positioning sequence are tightly packed. Dense promiscuous packing of fully wrapped nucleosomes rather than "beads on a string" with genic punctuation represents a distinct mode of DNA packaging by histones. We suggest that doublet histones have evolved for viral genome protection and may resemble an early stage of histone differentiation leading to the eukaryotic octameric nucleosome.
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