Noumeavirus replication relies on a transient remote control of the host nucleus

Abstract

Acanthamoeba are infected by a remarkable diversity of large dsDNA viruses, the infectious cycles of which have been characterized using genomics, transcriptomics and electron microscopy. Given their gene content and the persistence of the host nucleus throughout their infectious cycle, the Marseilleviridae were initially assumed to fully replicate in the cytoplasm. Unexpectedly, we find that their virions do not incorporate the virus-encoded transcription machinery, making their replication nucleus-dependent. However, instead of delivering their DNA to the nucleus, the Marseilleviridae initiate their replication by transiently recruiting the nuclear transcription machinery to their cytoplasmic viral factory. The nucleus recovers its integrity after becoming leaky at an early stage. This work highlights the importance of virion proteomic analyses to complement genome sequencing in the elucidation of the replication scheme and evolution of large dsDNA viruses.

The DNA Methylation Landscape of Giant Viruses

“…This result is coherent with what we know about the replication cycle of these viruses (53,61,62). Even if Melbournevirus temporarily requires nucleus functions to initiate its replication cycle (53), most of it then proceeds in the cytoplasm, without contact with the host DNA (53). This supports the non-involvement of Marseilleviridae R-M systems, as well as other encoded REases, in the recycling of the host DNA.…”

“…Figure 4 shows that the mel_015 REase gene is first transcribed between 30min and 45min post infection, followed by the mel_016 MTase gene expressed between 45min and 1h post infection. In addition, 6 proteomic data of the Melbournevirus virion from (53) confirm that the mel_016 MTase protein is packaged in the particle whereas the REase is not.…”

Analysis of a Marseillevirus Transcriptome Reveals Temporal Gene Expression Profile and Host Transcriptional Shift

“…(Boyer et al, 2009;Colson et al, 2013b). This virus family has been expanding over the last few years, with isolates from different regions around the world, such as Senegal, Tunisia, India, Japan, Australia, Brazil, and New Caledonia (Lagier et al, 2012;Aherfi et al, 2014;Doutre et al, 2014;Dornas et al, 2016;Takemura, 2016;Chatterjee and Kondabagil, 2017;Fabre et al, 2017). Along with other giant viruses isolated on amoebae, the Marseilleviruses are members of the proposed order "Megavirales, " which comprises the nucleocytoplasmic large DNA viruses (NCLDVs) (Colson et al, 2013a).…”

“…Once within the host cells, the Marseilleviruses establish large cellular structures (factories) for progeny virus production around 3 to 4 h post-infection (p.i. ), with genome replication being assisted by host nuclear proteins, morphogenesis occurs, and the viral progeny is released by cell lysis or wrapped inside giant infectious vesicles 8 h after infection (Arantes et al, 2016;Fabre et al, 2017).…”

Commensalism in theMimiviridaegiant virus family

“…After 1h of infection at 32°C, cells were washed 3 times with 30 mL of PPYG to eliminate the excess of viruses. For each infection time (every hour from 1h to 11h pi), 2.5 mL were recovered and we did include them in resin using the OTO (osmium-thiocarbohydrazide-osmium) method (52). Ultrathin sections of 90 nm were observed using a FEI Tecnai G2 operating at 200 kV.…”