( e 2). ...)Mammalian and Bacterial Expression in One Vector

Purification of CBP-Tagged Protein

figure 4

The GFP-CBP fusion protein was purified from bacterial cell lysates using the Affinity purification system. The purification was performed using the batch method described in the manual supplied with the kit. The calmodulin affinity resin with adsorbed GFP-CBP fusion protein was applied to a disposable column, washed and then eluted at neutral pH as specified in the manual. Aliquots of the IPTG-induced and uninduced bacterial lysate and the eluted fraction containing the fusion protein were resolved by SDS-PAGE and visualized by staining with Coomassie brilliant blue dye (figure 4). The size of the GFP-CBP hybrid protein is approximately 32 kDa, compared to that of the untagged 28-kDa GFP. The results (figure 4, lane 3) indicate that the small CBP affinity tag, located on the C-terminus of the protein, provides an effective and convenient way to purify the protein of interest from bacteria. In addition, the thrombin protease cleavage site allows cleavage to occur in the presence of thrombin for applications where removal of the affinity tag is desired. A time-course experiment showed that successful cleavage was achieved when the purified GFP-CBP fusion protein was incubated at room temperature with as little as 2 ng of thrombin in the presence of calcium. A representative cleavage profile of the GFP-CBP fusion protein is shown in figure 4. Full-length fusion protein was present in an aliquot that was removed immediately after addition of thrombin
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