Abstract: Provided herein is technology relating to the mutagenesis of nucleic acids, e.g., for directed evolution, and particularly, but not exclusively, to methods, compositions, and kits for producing nucleic acids and/or proteins comprising mutations and substitutions within specific target sequences.

Abstract: The present invention, in some aspects, provides methods, reagents, and kits for the functionalization of proteins on the surface of viral particles, for example, of bacteriophages, using sortase-mediated transpeptidation reactions. Some aspects of this invention provide methods for the conjugation of an agent, for example, a detectable label, a binding agent, a click-chemistry handle, or a small molecule to a surface protein of a viral particle. Kits comprising reagents useful for the generation of functionalized viral particles are also provided, as are precursor proteins that comprise a sortase recognition motif, and viral particles comprising such precursor proteins. Nucleic acids encoding viral proteins comprising a sortase recognition motif and expression vectors comprising such nucleic acids are also provided.