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We're looking at something that looks like a provirus in an organism's DNA, but it is not the result of a direct retroviral infection, because it is there in every cell, in exactly the same place.

It must have been inherited.

But what is it?

Well, it codes for viral proteins.
  • Reverse transcriptase, an enzyme involved in RNA->DNA transcription, a process which does not happen in eukaryotic (your) cells.
  • Envelope proteins, proteins that are found on the envelope of viruses
  • Viral proteases and other proteins that aren't natural to eukaryotes.
It has viral elements:
  • Viral promoters which are different from eukaryotic ones.
  • A distinctive gag-pol-env cluster of genes. the same cluster is seen in all retroviruses.
And another feature

The inescapable conclusion is that this is a provirus that has infected a germline cell of some ancestor, and any of its progeny that inherits it will have it in every cell of its body, and will pass it on to its offspring.