I would like to investigate protein-protein interactions. Both proteins have His-tags. How should I proceed?  

The labeling of the protein with the RED-tris-NTA 2nd Generation dye is reversible. Although the off-rate is very slow, the dye can “jump” from one His-tagged protein to another. Therefore, we recommend using one binding partner without His-tag. Typically, His-tags can be removed enzymatically from the protein during protein purification if a selective protease recognition sequence (e.g., TEV) was incorporated next to the His-tag.