HaloTag™ is a protein fusion tag which was genetically engineered to covalently bind a series of specific synthetic ligands. All ligands carry two groups, the reactive group and the functional/reporter group. The reactive group, the choloroalkane, is the same in all the ligands and is involved in binding to the HaloTag™. The functional reporter group is variable and can carry many different moieties including fluorescent dyes, affinity handles like biotin or solid surfaces such as agarose beads. Thus, HaloTag™ can serve either as a labeling tag or as a protein immobilization tag depending on which ligand is bound to it. Here, we describe a procedure for immobilization of HaloTag™ fusion proteins and how immobilized proteins can be used to study protein–protein and protein–DNA interactions in vivo and in vitro.
