in addresses that it can recognize.
Now of course they aren’t really addresses. Instead they are certain DNA sequences that Oct4 can latch onto.
DNA is made up of four bases—A, T, G, and C. These bases are arranged one after the other in a certain order. Each person’s set of DNA is a bit different.
Oct4 likes to bind to a certain set of letters—the sequence ATGCAAA. It turns out that this is close enough to a sequence found in the viruses that can come to life, ATGCCAA (the different base is marked in red).
The older, deader viruses do not have the same set of DNA in the same place. They either ACACAGA or ATATAGA. Neither of these are close enough for Oct4 to show any interest.
But having the right bit of DNA nearby isn’t enough. Oct4 has to also be able to “see” the DNA.
Can’t See the DNA for the Methylation
Most of the time the DNA Oct4 recognizes in these viruses is hidden away from it. Like those zombies buried in the ground in Thriller.
Instead of being buried though, the Oct4 DNA is shrouded behind a veil of something called methylation. Basically the cell adds small chemical groups called methyl groups to any DNA it doesn’t want a transcription factor to find. The methyl groups hide the DNA from the transcription factor.
When the researchers looked, they found that the viral DNA that Oct4 recognizes (as well as other DNA around it) is heavily methylated in cells where the virus is off. And those methyl groups are gone when the virus is on.
So to come to life the viruses need Oct4 to be around and for some of its DNA to lose some methyl groups. When this happens, Oct4 can swoop in and bring these viruses back to life.
The researchers have done a great job figuring out the how. Now they need to get cracking on figuring out the why.