"At first we thought something was wrong with our system," said Fedor.
But Fedor and Watson solved the puzzle. They discovered this riboswitch can bind both glucosamine-6-phosphate and glucose-6-phosphate. Each compound, however, produces opposite results. Binding glucosamine-6-phosphate induces self-destruction of the riboswitch and turns the glmS gene off; binding glucose-6-phosphate prevents self-destruction and keeps the glmS gene turned on.
"Scientists had long focused on the ability of riboswitches to recognize a single compound, but we have now found that riboswitches, or at least this one, can recognize multiple ones," said Watson.
"When glucose concentrations are high in a cell, it means that energy is abundant," explained Watson. "That is when cells would want to grow and divide and make more glucosamine-6-phosphate to build new cell walls. But when glucosamine-6-phosphate concentrations are high, then cells know to stop making more of this compound."
The glmS riboswitch function thus depends upon a balance between these twoand possibly additionalcompeting signals. "This kind of complex signaling had long thought to be the domain of just proteins," said Fedor. "This is another example of a function thought to belong only to proteins that we now know that RNA can do."
Fedor and Watson are now testing whether other types of riboswitches use this same mechanism. Unlike the glmS riboswitch, which self-destructs, most known riboswitches regulate the activities of their respective messenger RNAs by changing their three-dimensional structures in response to metabolite binding. The new shapes act to prevent the transc
|Contact: Mika Ono|
Scripps Research Institute