Viruses that infect archaea represent one of the most enigmatic parts of the virosphere. Their high diversity, along with their few structural and genomic similarities with bacterial or eukaryotic viruses, suggest that the mechanisms of virus-host interactions might be also unique. Saccharolobus polyhedral virus 1 (SPV1) belongs to the Portogloboviridae family and infects hyperthermophilic archaea from the genus Saccharolobus that thrive in terrestrial hot springs with temperatures of ~80°C and pH~2-3. Cryo-EM reconstruction of the SPV1 virion revealed that it consists of an icosahedral protein capsid surrounding an internal lipid membrane enclosing the circular dsDNA genome. The genome is complexed with the virus-encoded nucleocapsid protein which transforms the viral DNA into A-form. Unlike in other known viruses with icosahedral capsids, the nucleoprotein filament is wound up into a spherical coil. However, how the viral cycle unravels inside the host and how the virion is assembled remains a mystery. Preliminary data suggest that the virions are released from the cell without lysis, which is unprecedented for non-enveloped prokaryotic viruses. Here we study the SPV1 infection cycle and the host factors involved in its replication and release. This work should provide novel insights into the unique infection cycle of SPV1 and uncover new aspects of virus-host interactions in archaea.
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