Fig. 1: Split intein-mediated protein trans-splicing.

Highlighted are the key residues at both splice junctions. The first residue of the IntN fragment and the first residue of the ExtC harbor nucleophilic side chains (Cys, Ser, Thr), which are only Ser or Thr in cysteine-less inteins. The inlets illustrate the folding states of the intein fragments of an intein split at the endonuclease position. These states change from molten globule (N1 lobe) and disordered (N2 lobe) in the IntN fragment and disordered in the IntC fragment prior to the electrostatically driven association to the folded and intertwined complex in the assembled intein. ExtN, ExtC = N- and C-terminal exteins; PN, PC = N- and C-terminal precursor; SP splice product.