FIGURE 1.

Kan^R selection construct used to study intein specificity for flanking extein sequences. Kan^R was used as a reporter for protein splicing with the Npu DnaE intein and three additional extein residues flanking both its N and C termini. The sequence of the native extein is shown inserted into Kan^R site C. Underlined amino acids were simultaneously randomized. In the numbering scheme used in this paper, residues in the Kan^R protein, the variable extein positions, and the intein were numbered independently as indicated. Positions in the Kan^R protein were numbered as in the original protein, ignoring insertions.