The scope of this thesis was the in vivo and in vitro mediated maturation of antibodies by the protein AID. By simultaneous maturation and screening in each selection round it was possible to isolate affinity-optimized single clones against specific targets. HisAID731 was successfully produced recombinantly and the activity was detected. Single and double strand DNA which coded for thinly affinity sharkantibodies was treated with AID enzyme. The resulting mixture of Uracilcontaining DNA was amplified via PCR and the DNA mutantmixture was integrated in yeast cells. The resulting library was sorted for binding proteins with increased affinity against the target protein by highthroughput screening and affinityoptimized antibodies were isolated against the target protein in selection round two and three by yeast display. This evolutionary affinity maturation of antibodies fragments by the human activationinduced cytidine deaminase (AID) indicates that the antibody optimization from human B cells could be imitated in the S. cerevisiae.