A planarian nidovirus expands the limits of RNA genome size

  title={A planarian nidovirus expands the limits of RNA genome size},
  author={Amir Saberi and Anastasia A. Gulyaeva and John L Brubacher and Phillip A. Newmark and Alexander E. Gorbalenya},
  journal={PLoS Pathogens},
RNA viruses are the only known RNA-protein (RNP) entities capable of autonomous replication (albeit within a permissive environment). A 33.5-kb nidovirus has been considered close to the upper size limit for such entities; conversely, the minimal cellular DNA genome is ~200 kb. This large difference presents a daunting gap for the transition from primordial RNP to contemporary DNA-RNP-based life. Whether or not RNA viruses represent transitional steps on the road to DNA-based life, studies of… 

Structure and Expression of Large (+)RNA Genomes of Viruses of Higher Eukaryotes

Coronaviruses and closteroviruses have evolved to form flexuous helically symmetrical nucleocapsids as a mean to resolve packaging constraints and their similar properties likely have evolved convergently, along with the increase in the genome size.

The Curious Case of the Nidovirus Exoribonuclease: Its Role in RNA Synthesis and Replication Fidelity

Current understanding of ExoN evolution, structure, and function is reviewed and it is suggested that the enzyme is also critical for primary viral RNA synthesis, a property that poorly matches the profile of an enzyme that would merely boost long-term replication fidelity.

Replication of the coronavirus genome: A paradox among positive-strand RNA viruses

Planarian secretory cell nidovirus: The largest genome of RNA viruses

  • M. Zandi
  • Biology
    Reviews in medical virology
  • 2021
The genome size of PSCNV as the largest known nonsegmented RNA genome is 41.1 kb and can raise interesting questions about mechanisms which are used in gene expression by this virus.

Reduced Nucleoprotein Availability Impairs Negative-Sense RNA Virus Replication and Promotes Host Recognition

It is demonstrated that in addition to inducing a drastic decrease in genome replication, the antiviral host response in the absence of NP is dramatically enhanced, and the balance that negative-sense RNA viruses must achieve both to replicate efficiently and to avoid induction of the host defenses is demonstrated.

Origins and Evolution of the Global RNA Virome

A detailed phylogenomic reconstruction of the evolution of the dramatically expanded global RNA virome reveals the relationships between different Baltimore classes of viruses and indicates extensive transfer of viruses between distantly related hosts, such as plants and animals.

Protein Nucleotidylylation in +ssRNA Viruses

This review focuses on nucleotidylylation within the picornavirus supergroup of viruses, including the proteins that are modified, what is known about the nucleotidyl-transferase process and the roles that these modifications have in the viral life cycle.

The enzymatic activity of the nsp14 exoribonuclease is critical for replication of Middle East respiratory syndrome-coronavirus

An extensive mutagenesis study reveals an additional function for MERS- coV nsp14 ExoN, which apparently is critical for primary viral RNA synthesis, thus differentiating it from the proofreading activity thought to boost long-term replication fidelity in MHV and SARS-CoV.

A N7-guanine RNA cap methyltransferase signature-sequence as a genetic marker of large genome, non-mammalian Tobaniviridae

Multiple sequence alignments and structural analyses lead to the discovery of a putative Rossmann fold RNA methyltransferase in 10 Tobaniviridae members in Orf1a, an unusual genome locus for this gene, and a novel gene as a typical RNA-cap N7-guanine MTase with substrate specificity and active-site organization similar to the canonical eukaryotic RNA- cap N 7-GuanineMTase.



Coronaviruses: an RNA proofreading machine regulates replication fidelity and diversity.

Nsp14-ExoN is essential for replication fidelity, and likely serves either as a direct mediator or regulator of a more complex RNA proofreading machine, a process previously unprecedented in RNA virus biology, and will provide a robust model to investigate the balance between fidelity, diversity and pathogenesis.

Big Nidovirus Genome

Nidovirus sgRNAs are generated during a unique discontinuous transcription, which does not require breaking and ligation of phosphodiester bonds, as is the case with RNAs generated by splicing, and have been established to operate in coronaviruses and arteriviruses.

What we know but do not understand about nidovirus helicases

Discovery of an essential nucleotidylating activity associated with a newly delineated conserved domain in the RNA polymerase-containing protein of all nidoviruses

Bioinformatics analysis of non-structural protein 9 of the arterivirus equine arteritis virus revealed a nidoviral signature domain (genetic marker) that is N-terminally adjacent to the RdRp and has no apparent homologs elsewhere, and is proposed to have nucleotidylation activity.

Discovery of the First Insect Nidovirus, a Missing Evolutionary Link in the Emergence of the Largest RNA Virus Genomes

Rooted phylogenetic inference by Bayesian and Maximum Likelihood methods indicates that NDiV clusters with roniviruses and that its branch diverged from large nidoviruses early after they split from small nidviruses, a hypothesis that provides evolutionary support using comparative genomics involving the newly discovered first insect-borne ndovirus.

The 1.2-Megabase Genome Sequence of Mimivirus

The size and complexity of the Mimivirus genome challenge the established frontier between viruses and parasitic cellular organisms and this new sequence data might help shed a new light on the origin of DNA viruses and their role in the early evolution of eukaryotes.

Nidovirus transcription: how to make sense...?

Nidovirus transcription mechanisms are compared, the experimental systems used are critically assessed and, in particular, the impact of recently developed reverse genetic systems is discussed.

Novel divergent nidovirus in a python with pneumonia.

Analysis of genome organization and phylogenetic analysis of polyprotein 1ab suggests that this virus belongs to the subfamily Torovirinae, and results of this study provide novel insights into the genetic diversity within the order Nidovirales.

Thinking Outside the Triangle: Replication Fidelity of the Largest RNA Viruses.

This review compares the fidelity of small RNA viruses with that of the largest RNA viruses, the coronaviruses, and proposes models for regulation of coronavirus fidelity and discusses the implications of altered fidelity for RNA virus replication, pathogenesis, and evolution.

Three RNA cells for ribosomal lineages and three DNA viruses to replicate their genomes: a hypothesis for the origin of cellular domain.

  • P. Forterre
  • Biology
    Proceedings of the National Academy of Sciences of the United States of America
  • 2006
This work explores the possibility that three such independent transfers were at the origin of Archaea, Bacteria, and Eukarya, respectively, and explains why each domain has its specific DNA replication apparatus.