Several plasmids encoding this tag are available. It allows for easy insertion under the control of the natural promoter in yeast. This strategy may be useful, e.g., when some proteins belong to several complexes or when complex formation is transient. The TAP purification method involves the fusion of the TAP tag to the target protein of interest and the introduction of the construct to the cognate host cell or organism. If the protein belongs to a complex, it is generally preferable to maintain expression of the fusion protein at, or close to, its natural level.
Various strategies are available depending of the host cell or organism.
Obviously, if the goal is to purify associated proteins, the target protein should be expressed in cells or organisms expressing naturally the complex to ensure that the other subunits are also expressed. In brief, a PCR fragment containing a selectable marker and the TAP tag is integrated in the genome such as to fuse the TAP tag and the protein of interest. C-terminal tagging is often preferred because it should maintain expression of the target protein at its natural basal level. However, N-terminal tagging is also possible. The construction of the TAP-tagged target protein will depend on the vectors and transformation procedures available.