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A Truly Alive Virus
cyclop writes "Microbiologists are puzzled by the genome sequence of the giant Mimivirus. It seems this virus has even more genes than many bacteria, is able to synthesize its own proteins and therefore is, by definition, alive. 'We are seeing an organism here. There is DNA, RNA and plenty of proteins,' says Didier Raoult, who reports the work in this week's Science."
That geeks write "virii" in l33tspeak when they talk about computer viruses is one thing, but it's worse when this spelling pops up in scientific discussions. The plural is VIRUSES!
If you follow latin rules for constructing the plural form, it would still be viri with a single i at the end.
Avantslash: low-bandwidth mobile slashdot.
"This virus has a lot of DNA (the poxvirii do as well), but that does not mean it has a metabolism. Virii use their host's metabolism to produce proteins....."
I have this funny feeling you didn't RTFA before you decided that this was a worthless story.
From Nature: "It can make about 150 of its own proteins, along with chemical chaperones to help the proteins to fold in the right way. It can even repair its own DNA if it gets damaged, unlike normal viruses."
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It is quite simple, really. The virus enters the host cell. From there it uses the hosts machinery (enzymes, ribozyme, protiens, ect) to carry out the replication of the viruses DNA (or RNA whatever the case may be).
:)
However, the virus is not just bare DNA or RNA (gennerally). It also contains a protien coat on the outside that serves to hold and protect the virus genome. So this too must be made in great quantities to hold all the vast numbers of genomes that have just been copied.
So, in order for a virus to replicate in a cell, it must use the cells system to make BOTH the nucleic acid synthesis AND the protiens for the coat around the virus.
Since this process of protien sythensis uses energy, the virus IS using the cells matabolism to make protiens.
I hope that answers your question.
From the Science article: "Surprisingly, Mimivirus genome sequence now reveal genes relevant to all key steps of mRNA translation: tRNA and tRNA charging, initiation, elongation and termination, with the exception of ribosome components themselves." I'm sure many people knew that when the Nature News link said "Mimi carries about 50 genes that do things never seen before in a virus. It can make about 150 of its own proteins, along with chemical chaperones to help the proteins to fold in the right way." they meant within a host cell, but I'm sad to say I didn't get that right away. I really should have--there's a guy in the lab next door who does EM and crystallography on virus particles so I know that the inside of a virus capsid is ~crystaline DNA or RNA so no protein production would be expected to take place within the capsid itself.
Mimivirus does contain a lot of weird, weird stuff for a virus, including a number of DNA repair proteins, and truly bizarre, protein folding chaperones and a proline cis-trans isomerase. Doesn't make a damn bit of sense to me, but it'll be interesting to find out why it has them.
Oh yeah. You know it's news when Science gives you 13 freakin' pages for your stuff as opposed to the usual miserly 3.
A mutation in the protien structure of the viral coat might cause the abnormally large size (a reduction in the bonding angles, perhaps), allowing for the fused genome of the host bacterium and the original virus, along with various key molocules from the bacterium to all be packaged into the virus, instead of just the viral DNA alone.
It's long been known that the viral coat proteins can only accept a certain amount of DNA to be packed inside them. A good example of this is the use of Lambda libraries 10 years or so ago which could only hold maybe 10 to 15kb which had to be removed from the viral genome first to make space. The idea that a mutation which allows this virus to hold more is a good one. If you have the room to store something, and events such as integration, excision and recombination allow for your genome to increase in size when infecting a cell, then the genome will increase in size. Just like anything in life: glove compartments, houses, hard drives - when you get more space you end up filling it rather quickly.
But to say this virus is, or even could be either evolving towards bacterialhood or evolving away from it is quite ludicrous. Sure, you can have a bacteria with less than 300 genes, but those themselves are forced to live as obligate parasites. Even if this virus did manage to get just the right combination of genes which could allow it to "live" outside of a host, it would be like giving me blueprints to build a radio on a deserted island - useless, the virus doesn't have the machinery to use the information itself.