Interviewee: Walter Gilbert. Walter Gilbert describes how they did the experiment to isolate the lac operon repressor. (DNAi Location: Code > Controlling the code > Players > Walter Gilbert > Isolating the repressor)

We knew that the molecule should interact with the sugar that was coming into the cell. And so we could use a radioactive form of that sugar to try to look for a molecule that it interacted with inside the bacterial cell. We knew that interaction was, we knew something about the strength of that interaction and we could actually decide that interaction was probably too weak for us to be able to see it. So Benno Muller-Hill modified the bacteria, made a mutation, a genetic mutation, that changed the way in which the repressor bound to the small molecule we call an inducer, and made a mutation so the repressor now worked more tightly, bound to the inducer at a lower concentration. And then we took those bacteria, and looked for the interaction between the, a protein and the small molecule, by using a radioactive small molecule, and asking actually, we put the protein inside a little sack that the small molecule could move in and out of, could we find an excess of molecules bound inside the sack because they were attached to the protein. And we actually made that experiment work.

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