 inteins self - splice from precursor polypeptides to reconstitute functional proteins . here 
 we describe inteins as redox - responsive switches in bacteria . 
 regulation was achieved by engineering a disulfide bond between the intein s catalytic cysteine and the flanking polypeptide . 
 this interaction was validated by an x - ray structure , which includes a transient splice junction . 
 a natural analogue of the designed system was identified in pyrococcus abysii , suggesting an unprecedented form of adaptive , post - translational regulation . 
Supplementary Material