Genetic Code Expansion Facilitates Position‐Selective Modification of Nucleic Acids and Proteins

Transcription and translation obey to the genetic code of four nucleobases and 21 amino acids evolved over billions of years. Both these processes have been engineered to facilitate the use of non‐natural building blocks in both nucleic acids and proteins, enabling researchers with a decent toolbox for structural and functional analyses. Here, we review the most common approaches for how labeling of both nucleic acids as well as proteins in a site‐selective fashion with either modifiable building blocks or spectroscopic probes can be facilitated by genetic code expansion. We emphasize methodological approaches and how these can be adapted for specific modifications, both during as well as after biomolecule synthesis. These modifications can facilitate, for example, a number of different spectroscopic analysis techniques and can under specific circumstances even be used in combination. Expediated by expansion: Using expansion of the standard genetic code in both transcription and translation, modifiers can be introduced into either proteins or RNA to facilitate site‐specific labeling and modification. Non‐natural base pairs as well as systems for the incorporation of non‐canonical amino acids have been established and optimized, and harness the intrinsic specificity requirements of natural machineries for biosynthesis of both proteins and RNA.