Hi Yazhou,

since you didn't mention which kind of TAP you want to perform its pretty difficult to give you some useful advice. But nontheless, using a high affinity Tag like Protein A combined with a CBP Tag should usually yield a nice and pure protein. The only problem is that it really depends on the protein you want to purify, because they all tend to behave differently and you will most probably have to empirically optimise conditions anyhow.

I would suggets, that you really check all fractions carfully in the beginning, because later its much easier to sort out the critical point of the purification.

Best Kai