How the genome fills its virus


Rebecca Pool

Wednesday, June 5, 2019 - 09:30
Image: Virus with liquid crystal genome within [Juha Huiskonen]
In a world first, researchers from the Universities of Helsinki and Oxford have revealed how a virus genome is condensed inside the capsid of a virus.
Using cryo-electron microscopy, Professor Juha Huiskonen from the Helsinki Institute of Life Science and colleagues captured tens of thousands of images of highly purified viruses and then combined these into three-dimensional models.
In this way, they could observe the proteins that make up the shell of the virus but also trace the nucleic acid genome inside the protein shell.
“The degree of condensation is remarkable,” highlights Huiskonen. “To illustrate, if the virus was the size of an exercise ball and the viral genome was thick manila rope, there would be almost 70 metres of such rope stuffed inside the ball.”
Characterising the genome of mature virions is pivotal to understanding the highly dynamic processes of virus assembly and infection.
With this in mind, the researchers acquired genome data from a tri-segmented bacteriophage ɸ6 of the Cystoviridae family over a single four-day session using a 300 kV Titan Krios cryo-TEM equipped with a Falcon II direct electron detector, both manufactured by Thermo Fisher Scientific.
RELION software was used to reconstruct the genome.
The genome was seen to form a liquid crystal, a highly condensed and ordered state of matter that is still fluid.
According to the researchers, the fluidity of the genome may be required to allow expression of the viral genes in the confines of the viral capsid, but it is still an open question how the virus genome doesn’t get entangled in the process.
Huiskonen and colleagues intend to address this very question in a follow-up study.
“When the viruses are carrying out their work, they can be observed at different states. This way we can gain an even better understanding of how these fascinating nanomachines function,” says Huiskonen. “The motivation of the study was to increase our basic understanding of viral replication, but in the long term this may contribute to tackling viral disease.”
Research is published in Nature.
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