Abstract: The present invention combines PCR™ mutagenesis with in vitro transcription/translation and ELISA for the rapid generation and characterization of protein mutants. The PCR™ products are used directly as the template for the in vitro transcription/translation reactions and because no cloning steps are required, the in vitro saturation mutagenesis of one residue can be completed in duplicate within a week by a single investigator. This high throughput enables the saturation mutagenesis of numerous residues of interest, a process that can be described as in vitro scanning saturation mutagenesis. Compositions and methods of use of such a process are described herein.