Tethered bandshift assay and affinity purification of a new DNA-binding protein.

DNA-binding proteins can be purified by their affinity for probes with specific sequences that are tethered to magnetic beads. A restriction site at the end of the tether allows release of probe with factor still on it. This probe with bound factor can be bandshifted directly to compare to bandshifts in whole extracts. This method correlates purified factor seen indirectly by bandshift with factor that is purified and released, because they are the same.