Monday's Molecule #31

 
Today's molecule is complicated but it makes a lot of sense if you know your basic biochemistry. We don't need a long complicated name this time. It's sufficient to simply describe what you're looking at and why it's significant. You have to identify the key residue to get credit for the answer.

As usual, there's a connection between Monday's molecule and this Wednesday's Nobel Laureate(s). This one is an obvious direct connection. Once you have identified the molecule you should be able to name the Nobel Laureate(s).

The reward (free lunch) goes to the person who correctly identifies the molecule and the reaction and the Nobel Laureate(s). Previous free lunch winners are ineligible for one month from the time they first collected the prize. There are no ineligible candidates for this Wednesday's reward since recent winners (including last week's winner, "Kyo") have declined the prize on the grounds that they live in another country and can't make it for lunch on Thursday (a feeble excuse, in my opinion, haven't you heard of airplanes?).

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UPDATE: The molecule is the lariat structure of the RNA splicing intermediate. The key residue is the adenylate residue that's joined through its 2′ hydroxyl group to the 5′ end of the intron [see RNA Splicing: Introns and Exons]. The Nobel Laureates are Rich Roberts and Phil Sharp. (See the comments for an interesting anecdote concerning the discovery of this molecule.)