I mean, ERV!
I mean, NIRV!
As my blag tagline goes, ‘If we are made in Gods image, God is made of gag, pol, and env’, the components of retroviruses. Our, and other organisms, genome is inhabited by lots of bits of selfish DNA, including retroviruses.
But retroviruses are not the only group of viruses who have made themselves right at home in our DNA– once we started looking, it turns out that there are allllll kinds of viruses just hangin out!
Its not hard to imagine how endogenous retroviruses came to be– A retrovirus accidentally infects an egg/sperm (probably a sperm!), which goes on to create a viable organism, which then permanently has the retrovirus in its DNA, which gets passed on to its offspring.
But what about the DNA viruses? What about the RNA viruses? They shouldnt really be able to become endogenized like a retrovirus, and yet, theyre there.
The folks in this paper found Sigma Virus in the genomes of the Drosophila genus (fruit flies). Sigma Virus is related to rabies, in that they are both rhabdoviruses, but infected fruit flies dont go around foaming at the mouth biting other fruit flies. The infection isnt *that* big of a deal, and it is normally passed on to offspring via infected eggs/sperm.
Hey… that egg/sperm thing means it kinda makes sense for fruit flies to have endogenous Sigma Viruses… except that these are not retroviruses. They are negative strand (backwards) RNA viruses. The ones in the genome are called NIRVs– Non-retroviral Integrated RNA Viruses.
… So how the heck does a RNA virus get into a genome?
There are any number of ways it could have happened, and like Creationists are fond of saying ‘YOU WERENT THERE! YOU DUNNO!’ And unfortunately, since these integrations normally happened a long long long long time ago, and they are not exactly favorable events, both the endogenous viruses and the stuff surrounding them have mutated a lot over time. So its hard to really nail down how these Sigmas are getting in.
Well, we might not know how ALL of them got in, but at least three insertions were preserved enough that these study authors figured out that these Sigma insertions have a fun history–
On two locations in the 3R chromosome, and one location on the X chromosome, there are Sigma viruses snuggled up inside of endogenous retroviruses! Its like ERV genomes are just giving the Sigma genomes a warm hug.
This implies that while the endogenous retrovirus was just derping around, being selfish DNA, the reverse transcriptase accidentally hopped onto the Sigma Virus RNA instead of the retrovirus RNA (RT hops all over the place during reverse transcription).
It then had to hop back over to the retrovirus RNA to successfully complete the reverse transcription and insertion process!
The Sigma Viruses are pirating the ERV pirate to get into the genomes (at least in these three cases)!
But it gets even weirder– the ERVs the Sigmas are pirating? They do not code for a reverse transcriptase protein.
Which means the ERVs had to pirate an RT from other ERVs!
Pirates all the way down, lol!!
An absolutely ridiculous series of events had to take place for these three Sigma Viruses to become NIRVs. An absurdity that completely supports evolution.