| Summary: | An efficient self-cleavable purification tag could be a powerful tool for purifying recombinant proteins and peptides without additional proteolytic processes using specific proteases. Thus, the intein-mediated self-cleavage tag was developed and has been commercially available as the IMPACT™ system. However, uncontrolled cleavages of the purification tag by the inteins in the IMPACT™ system have been reported, thereby reducing final yields. Therefore, controlling the protein-splicing activity of inteins has become critical. Here we utilized conditional protein splicing by salt conditions. We developed the inducible intein-mediated self-cleaving tag (IIST) system based on salt-inducible protein splicing of the MCM2 intein from the extremely halophilic archaeon, <i>Halorhabdus utahensis</i> and applied it to small peptides. Moreover, we described a method for the amidation using the same IIST system and demonstrated <sup>15</sup>N-labeling of the C-terminal amide group of a single domain antibody (V<sub>HH</sub>).
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