This structure is called a "kissing loop" and I find that name just a bit odd, given the source of the structure.
Now, here's the puzzle: Why would I say that the name "kissing loop" is ironic?
I wasn't familiar with this structure, but having read a bit about it now, it's seriously cool!
It seems it was first discovered in HIV (although it's apparently present in all retroviruses?). And of course, HIV is sexually transmitted. Hence the irony in the word kissing.
I was puzzled for a while by the ball-and-stick portions of the figure. I could see they weren't individual nucleotides of the RNAs, but couldn't tell what they were. Then I found the structure here.
The ball-and-sticks are molecules of the aminoglycoside antibiotic ribostamycin. That makes this even more cool. I had no idea that an antibiotic that normally targets bacterial ribosomes can also bind to a structural motif in HIV RNA. Looking over the discussion in the paper in question, I can see this is not a very new finding (some refs as early as 1993), but it's new to me.
Great post! Thanks!
Glad you liked it! There are lots of amazing things that happen with RNA, this is only a peek behind the curtain.
Oh, I know it! I really like the unusual things that nucleic acids do. There are just too many of them to keep up with, and retroviruses aren't normally on my radar screen.