Fig. 1.

Protein trans-splicing of the Npu DnaE split intein. (A) Schematic depicting the ultrafast trans-splicing reaction of the Npu DnaE split intein under its native extein context. Npu is shown embedded within the α subunit of DnaE, flanked by its native extein residues (“AEY” at the N-extein and “CFN” at the C-extein). The +1 and +2 positions of the C-extein are highlighted in red. (B) Schematic depicting the splicing reaction of the Npu DnaE intein embedded within a target protein of interest (POI). The reaction is shown in the context of an Ala₊₂ C-extein residue, which is unfavorable for splicing activity.