Viral origins?

[genovese]

Since viruses appear to originate since the beginning of life I cannot help but wonder if there was another reason for their presence other than being mere parasites.

Could they have been early attempts at "sexual" reproduction (hybridizations) rather than asexual (cloning) reproduction? Could tRNA, or a similar bit of RNA, have been made to invade other organisms in order to mix genetic information?

I would be grateful for information regarding any thoughts on this subject.

[david23]

organisms that use sexual reproduction to inevitably increase variability of its genome are mostly multicellular organisms. Single cell organism and of course more simpler viruses do not need to and cannot use the complex sexual reproduction methods. Also a virus with a limited error proofing mechanism can easily evolve a lot faster than any multicelluar organism.

Viruses can sometimes cross transmit their genome with another virus most likely have to be similar during transduction of the same cells.

Also again there is the lack machinery to do anything on their own so they will always be parasites

[genovese]

Thanks for that information.
Forgetting the reproductive side of my question, could virus particles have been made from unicellular or multicellular organisms "in error" from bits of RNA machinery, which then acquired the protein coat to invade other, but antigen-similar organisms, thus leading them to become infective particles in their own right?

[david23]

What you are saying is possible, but when asked of other scientists this, the usual answer is I dont know.

Lets see what we can make your idea possible. Lets go with a very simple DNA virus without any envelope even though RNA viruses are supposed to be older. A piece of DNA within a host has to have a bunch of nucleases that specific cuts that part out. And that part of DNA must have the nuclease genes in them. That part of the DNA must also have genes for a protein coat, which only a virus has. There should also be genes for anchor protein to attach to cells, so ok more mutations.

So the attachment proteins and the coat would have to be acquired in some way.

There would also be enzymes for protease, integrase equivalents. The integrase enzymes would have to come from somewhere.

There are some more essential enzymes I cant think of right now, but basically they either have to mutate from the host enzyme homologs or acquire them somehow.

[genovese]

Thank you for your reply -all very interesting.
I chose RNA over DNA because, as you say, it is an older molecule. Also it has properties of acting as a catalyst – which makes it a very interesting molecule in the early days of evolution.

As for acquiring a protein coat- I would have thought that a lot of that information was already coded for in the genes of the host to make its own cell membrane perhaps? The viral coat would have to have the same antigens as the cell host so as to be able to target a similar cell.

That is why I thought that the production of the virus particle might have been an early evolutionary attempt at sexual reproduction, which then went wrong or which was just replaced by a more effective method.

[Darby]

It’s an interesting idea, almost as if particular plasmids went out out of the "sharing" business and into the "self-perpetuation" business.

I guess the pertinent question is, what sorts of comparisons one can make between viral nucleic acids and cellular – does it seem to be a different sort, or possibly derived? And could derivation be explained as just an evolutionary trend toward compatibility with the host cell?

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