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| Marseillevirus By: Swiss Institute of Bioinformatics |
Download Episode (6 MB, 6.5 minutes)
Show notes:
Microbe of the episode: Caulobacter maris
News item
Journal Paper:
Erives AJ. 2017. Phylogenetic analysis of the core histone doublet and DNA topo II genes of Marseilleviridae: evidence of proto-eukaryotic provenance. Epigenetics & Chromatin 10:55.
Other interesting stories:
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Episode outline:
- Background: Giant viruses more and more discovered
- Usually found in amoebas or other small eukaryotes
- Have large genomes with many genes of unknown function
- Set up virus-making factories in host cells with their own proteins
- Many giant virus genes related to host genes, perform similar functions but in own ways
- Better control to hijack host metabolism
- Family called Marseilleviridae even have genes for core histones
- Help organize DNA into tightly packed chromosomes
- Where did they come from? And why does virus need them?
- What’s new: Now, Albert Erives, publishing in Epigenetics & Chromatin, has discovered that these giant virus histone genes, and other genes, seem to have branched off very early in the history of all eukaryotes!
- Methods: Compared gene sequences of virus histones with eukaryotes and archaea
- See where they fell in family tree based on sequence differences: phylogenetics
- Consistently fell outside eukaryote group (containing yeast, insects, protists)
- But archaea fell outside group of eukaryotes+viruses
- So viruses group with eukaryotes relative to outsiders, but are unique and different within
- Same results with virus's DNA structuring enzymes, like topoisomerase
- Twists DNA into coils to pack tighter
- Virus genes inside eukaryote group relative to archaea, but separate
- Summary: Giant viruses encode proteins usu found only in non-bacterial DNA structuring, but their genetic origins are separate from known eukaryotes and archaea; separate branch on tree of life
- Applications and implications: Kinda like going to Mars and finding strange alien organism
- That then turns out to be related to us
- Either came from Earth to Mars long ago
- Or maybe life on Earth came from Mars?
- Or both came from a third source!
- Except not quite that exciting
- Viruses obviously related to the rest of tree of life
- But not always clear exactly how
- Each gene could come from different source though; good at moving DNA around
- Possible these genes were taken from something else more familiar, more recently
- But based on sequences, seems more likely that the viruses kept them since splitting off
- Kind of window, or part of a key to a lock, into how life looked early in eukaryote history
- Not too meaningful alone, but by comparing with eukaryotes, can learn things
- Interesting to know if/how these histones and such function differently
- Benefit to virus to use them?
- Very interesting
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