Fig. 1.

(a) Schematic representation of protein splicing in cis and trans. A cis-splicing intein is naturally or artificially split into two fragments. Upon association of the two intein fragments, protein trans-splicing (PTS) is induced by the formation of an active intein structure. This might also result in N- or/and C-cleavages. (b) Distribution of the split sites from the previously reported split inteins. The split sites are divided into ‘active’ (blue) and ‘inactive’ (red) and are classified by the new split intein nomenclature and blocks. The secondary structures are indicated by black arrows (β-sheets) and gray rectangles (helices). Lines below the secondary structures show the conserved blocks: A, B, F and G. Δ and EN represent endonuclease domain insertions found in many inteins.