US Patent 7476500 In vivo selection system for enzyme activity

The present invention provides in vivo systems in which activity of a biological cleavage enzyme, such as a site-specific recombinase, a homing endonuclease, or an intein, is linked to cell viability and therefore can be selected. The invention further provides methods of making cells in which the activity of a biological cleavage enzyme is linked to viability, as well as methods of identifying new biological cleavage enzymes, including enzymes having altered site specificity, using such cells.