HOUSTON -- (Sept. 22, 2009) -- The tools of biochemistry have finally caught up with lactose repressor protein. Biologists from Rice University in Houston and the University of Florence in Italy this week published new results about "lac repressor," which was the first known genetic regulatory protein when discovered in 1966.
Using cutting-edge techniques, the scientists tied together two segments within individual molecules of lactose repressor protein. They then measured the ability of these tethered molecules to form DNA loops to determine how flexibility within the protein influences the extent to which these loops can form. The results appear online this week in the Proceedings of the National Academy of Sciences.
"It's become increasingly clear that many proteins are highly flexible and able to form different types of structures when they interact with something else, often another protein or DNA," said study co-author Kathleen Matthews, Rice's Stewart Memorial Professor of Biochemistry and Cell Biology, who began studying lactose repressor protein in 1970. "That's true for lactose repressor in binding to DNA, making it a good candidate to learn more about the process of DNA looping because it's a relatively simple and well-studied protein."
With proteins, it is impossible to separate form from function; they do what they do because of their shape. That said, it is also unusual for scientists to get a clear picture of what a protein looks like in its native environment. For example, the general structure of lactose repressor has been known for some time, but questions have remained about how it flexes and moves inside a living cell.
Lactose repressor is a V-shaped bacterial protein that has two arms connected by a central hinge. Each arm has a sticky tip that's designed to grab hold of DNA. When each arm "sticks" to a different site within a single DNA molecule, a loop forms, creating a "pinched-off" section
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