An in vivo selection system for homing endonuclease activity.

Homing endonucleases are enzymes that catalyze the highly sequence-specific cleavage of DNA. We have developed an in vivo selection in Escherichia coli that links cell survival with homing endonuclease-mediated DNA cleavage activity and sequence specificity. Using this selection, wild-type and mutant variants of three homing endonucleases were characterized without requiring protein purification and in vitro analysis. This selection system may facilitate the study of sequence-specific DNA cleaving enzymes, and selections based on this work may enable the evolution of homing endonucleases with novel activities or specificities.