Encyclopedia of Experiments: Biological Techniques
A subscription to JoVE is required to view this content.
Transcript
Transcription factor, TF, is a protein that binds to a gene's specific DNA region and regulates transcription.
To measure TF-DNA interactions by fluorescence anisotropy, take a multi-well plate. Add molten gel mixed with a buffered solution, containing known concentrations of fluorophore-tagged reference DNA comprising a TF-binding site and a higher concentration of TF molecules, to the well and incubate.
As the labeled reference DNA distributes in the gel, a higher TF molecule concentration ensures all the DNA molecules are TF-bound. Add a buffered solution containing unlabeled competitor DNA with a single-point mutation.
Analyze the plate's gel using high-performance fluorescence anisotropy microscopy.
Polarized light excites the reference DNA-bound fluorophore, which reorients due to molecular tumbling and emits multi-directional depolarized light ― a phenomenon called fluorescence anisotropy, FA.
Upon binding to TF, the reference DNA-bound fluorophore's molecular weight increases and it tumbles slower, emitting more polarized light that increases FA.
The unlabeled competitor DNA diffuses across the gel matrix over time, forming a high-to-low concentration gradient. A higher unlabeled competitor DNA concentration displaces the labeled-reference DNA, binding itself to TF. The released labeled-reference oligomers tumble faster, decreasing FA.
Plot the fluorophore's FA and the competitor DNA's concentration gradient over time ― which decreases as more competitor DNA molecules displace the reference DNA.
