Gel shift assays can be used to assay protein binding activity to DNA or RNA.
This allows the identification of whether the two components (the nucleic acid and the protein) interact, through gel electrophoresis.
The protein-DNA complex, if successful in its formation, will more more slowly through the gel than just the protein or DNA individually. Relative binding affinity can also be determined by the relative band sizes - allowing the identification of how strong the interactions are.