gether, the absence of Gal4-RE-binding factors and Gal4 consensus recognition sites in higher eukaryotes, the lack of cellular toxicity of 4OH-tamoxifen and of estradiol and the strong repressive activity of 4OH-tamoxifen-bound GalER

The Mycobacterium xenopi gyrase A mini-intein has been engineered to yield a controllable N-terminal or C-terminal, single-splice-junction autocleavage element. When combined with an affinity tag, these modified mini-inteins can be used to purify target proteins after a single combined chromatography/cleavage step. Cleavage at the intein N terminus was induced with thiol reagents, while cleavage at the intein C terminus was induced by a temperature shift to 16°–25°C. Different preferences for the residue immediately preceding the intein were observed during thiol-induced, N-terminal splice-junction cleavage of the M. xenopi gyrase A mini-intein vs. the Saccharomyces cerevisiae vacuolar ATPase, subunit A (VMA) intein present in the IMPACT purification system. Furthermore, the M. xenopi gyrase A mini-intein Cterminal autocleavage vector allows isolation of polypeptides with N-terminal cysteine residues that are active in the Intein Mediated Protein Ligation method of protein semisynthesis.