Directed Evolution of the Substrate Specificities of a Site-Specific Recombinase and an Aminoacyl-tR

A variety of in vivo selection and screening methods have been developed for the directed evolution of protein function. Typically, in vivo selection strategies involve the identification of new binding or catalytic functions based on their ability to confer a selective growth advantage on the host cell (usually Escherichia coli ). In vivo screening approaches differ from selections in that screening involves the detection of a desired activity on the basis of its ability to produce an identifiable signal in an activity assay.