© GEORGE RETSECK

Researchers modified an endogenous Bacteroides promoter sequence to be inducible—it can be turned on or off in mice by adding (right) or omitting (left)  anhydrotetracycline (aTC) to the animal’s drinking water. The aTC binds to the TET repressor protein (yellow), thereby preventing its suppression of gene expression. As a proof of principle, the researchers integrated the modified promoter upstream of a sialidase gene in the bacterium’s genome, and showed they could control the enzyme’s activity in mouse intestines.

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