As we suffer through the end of cold and flu season here in the great white north (Canada) I’m well aware of the effects of viruses. I’ve often wondered why it is that viruses exist in the first place.
Some may say this question is as naive as asking why do mosquitoes exist? Viruses, after all, can be thought of as simple cellular parasites, using our cells to reproduce and spread. Just the same mosquitoes don’t require an intimate knowledge of the workings of our cells, indeed the very core of our cells, to function. Given that viruses are able to exploit our cellular processes suggests that they may themselves be part of a cellular process.
If you consider sperm, they are essentially packages of DNA with an outboard motor. It isn’t a huge stretch of the imagination to imagine that viruses may be a method of information exchange. In the bacteria world, genomic information exchange (aka sex) occurs via the exchange of ‘plasmids’. Plasmids are circular bands of DNA which can readily be exchanged and recombined among bacteria. Plasmids are typically not parasitic but more symbiotic and convey useful traits such as antibiotic resistance. Viruses can also behave in this way. Endoviruses, viruses which incorporate themselves back into their hosts DNA, could be used as a method of information exchange and transfer.
I’ve often considered an effective method for wiping human viruses off the planet in one felled swoop. Viruses hijack cellular factories called ribosomes which manufacture proteins for us. When infected, our ribosomes execute the viral code which in turn produces more viruses. To disable all human viruses wouldn’t require much effort at all. Viruses and ribosomes speak the language of RNA which is a derivative of DNA. Ribosomes currently have no good way of differentiating between human RNA and viral RNA. (As an aside, RNA sequences that contain siRNA (small interfering RNA) segments are a good clue that the sequence is viral. This causes the cell to act to destroy such sequences. However, we all still get sick, thus it clearly isn’t 100% effective.) To effectively wipe out all human viruses all we would need do is add some well known key to all human RNA sequences. The ribosome would then reject all sequences missing this key. This would instantaneously wipe out all human viruses (which would lack this key).
So why don’t we do this? First it’s beyond our current technology to alter our DNA in such a fashion, but it won’t be long before it’s within our grasp. The question is: would we want to? Elements of our genome already act like viruses. Genes called transposons effectively jump from one part to another. Disabling viruses may somehow preclude a vital source of information exchange. In our oceans, bacteria ‘suffering’ from viral infections work to produce oxygen and sequester carbon dioxide. Without this viral ‘infection’ it’s likely life as we know it couldn’t exist on earth.
So the next time you’re run down with a virus, consider that you’re merely the victim of a side effect of a process essential to life on earth. Perhaps this is why we say “Bless you” when someone sneezes? 🙂
So, in destroying human viruses, you’re speculating that we might also destroy transposons? Would this really wipe out the human species, or would it just make us less diverse? (And thus more prone to being wiped out by something else.)
Sort of… I don’t think we’d eradicate transposons because they have a human source so they’d have this ‘key’ to the ribosomes. I was speaking more generally that in eliminating human viruses we may be eliminating a method for information (gene) exchange.
I didn’t mean to suggest that eliminating viruses would eliminate the species. I was just suggesting that like, the story of antibiotics, we needn’t consider bacteria nor viruses as simply ‘the enemy’. The true story is more complicated. Bacteria and viruses aren’t the enemy and the ultimate cure to illness is learning to come into symbiosis with them rather than the dysbiosis which results when we merely try to eradicate them.
I don’t think your scheme would be possible. The RNA tag needs to be transcribed, not added later (since then it would be added to viral RNAs transcribed in the cell), so it actually needs to be inserted into the DNA. That means modifying every single transcribed open reading frame in the entire genome. You additionally need to add a means of detecting this tag, so that means perhaps adding a novel protein or even whole set of proteins to the translation machinery–good luck with integrating that. This massive genomic overhaul would have to be done on every human on the planet in one fell swoop, because otherwise if a person without the overhaul bred with a person with the overhaul, their offspring would either die or have major systemic problems. Then there’s the addition of many opportunities for new disease if a mutation drops the tag on a gene. Add in the additional problem of evolution being more clever than you (Orgel’s second rule) and the eventual acquisition of this tag by a virus is inevitable. If this were remotely possible, evolution would have invented it already!
Lateral gene transfer is not terribly important for multicellular organisms. The only cases of viral transfers of genes that we know about are oncogenic (causing cancer). Viruses have been instrumental in causing mutations, which can be fuel for evolution, and we actually domesticated one viral gene in our evolutionary history that is active in placental development.
Transposons also have been useful in history, but for their role in adding DNA (fuel for evolution) and screwing up genes, sometimes making new ones. Transposons cannot transmit DNA from individual to individual because they do not move outside the cell.
siRNA is just small interfering RNA. In invertebrates it is generated from double-stranded viral RNA (normal RNA is single-stranded) by the action of a RNA-cutting molecule called Dicer, and the short RNAs are then used by the RISC complex to degrade complementary viral RNA. However in mammals the response to double-stranded RNA goes through Toll-like receptor 3 and the RISC complex is actually used for making micro RNAs that help control genomic gene expression.
There are several major classes of viruses that have very different lifecycles, and there is no magic bullet that can destroy every single one.
>I don’t think your scheme would be possible. The RNA tag needs to be >transcribed, not added later (since then it would be added to viral RNAs >transcribed in the cell), so it actually needs to be inserted into the DNA.
Actually the gene that codes for DNA transcriptase and Ribosomes would be the only genes that need be altered. With an altered DNA transcriptase, a leading key sequence could be added for every transcribed mRNA. The gene that codes for ribosomes would also need to be altered to accept only mRNA with the leading key sequence.
>Add in the additional problem of evolution being more clever than you >(Orgel’s second rule) and the eventual acquisition of this tag by a virus is >inevitable.
Perhaps there is a simple misunderstanding of my intent here. I mean to suggest that in the near future we’ll be able to engineer this key. If any viruses manage to guess the key… we’ll simply change it until all viruses are eliminated. I’m not talking about evolution here, I’m talking about engineered genomes.
>If this were remotely possible, evolution would have invented
>it already!
No, evolution produces good enough solutions, not the best solutions. This is why we don’t see any animals with wheels.
>Lateral gene transfer is not terribly important for multicellular organisms. >The only cases of viral transfers of genes that we know about are >oncogenic (causing cancer).
Correct. I was suggesting that viruses, human viruses, or multicellular organism viruses were the biproduct of viruses that were useful to our single celled predecessors. Ie, we came from bacteria who use viruses for genomic exchange and as a result, we have viruses which may or may not (likely not) for genomic exchange.
>Transposons cannot transmit DNA from individual to individual because they do not move outside the cell.
Agreed. I was suggesting in transposons we see another value of ‘moveable’ bits of genomic information. The subtext to that remark is that if we had the power to disable viruses, we should execute it with caution as we may subvert a valuable mechanism for information exchange.
>There are several major classes of viruses that have very different >lifecycles, and there is no magic bullet that can destroy every single one.
Yes, but the large majority are RNA viruses which could be disabled if ribosomes refused to execute their instructions.
Thanks for the feedback…MCW
“With an altered DNA transcriptase, a leading key sequence could be added for every transcribed mRNA. The gene that codes for ribosomes would also need to be altered to accept only mRNA with the leading key sequence.”
The problem is RNA viruses transcribe their mRNA in the cell, and this would add on the tag. You might mildly inconvenience positive-stranded RNA viruses until they could generate more transcripts from their genome, but negative-stranded would proceed about their business as usual. Additionally you don’t touch retroviruses and DNA viruses.
“I’m not talking about evolution here, I’m talking about engineered genomes.”
Again, Orgel’s second rule says evolution is more clever than you. Genetic engineering is a way to jump ahead of evolution, but evolution always catches up.
“No, evolution produces good enough solutions, not the best solutions.”
You’re proposing a solution that would use two simple (according to you, according to me way too complicated to ever work) modifications and you think evolution would not have hit upon this already if it were possible? The types of tags you talk about are in use for many purposes in cells, and viruses have co-opted these.
“Correct. I was suggesting that viruses, human viruses, or multicellular organism viruses were the biproduct of viruses that were useful to our single celled predecessors.”
I think viruses were primarily parasitic from the beginning, although sometimes being subverted.
http://www.physorg.com/news127558509.html
A useful virus 🙂