Monday, July 23, 2018

BacterioFiles 348 - Huge Host Hackers Have Historic Histones

By: Swiss Institute of Bioinformatics
This episode: Giant viruses produce DNA-packing proteins that seem to have branched off from eukaryotes far back in evolutionary history!

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.

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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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