Abstract: MATH/CHEM/COMP 2002, Dubrovnik, June 24-29, 2002

Experiments and Prospects for Changes on the Interpretation of the Genetic Code

Nediljko BudiSa, Robert Huber, and Luis Moroder

Max-Planck-Institut fuer Biochemie, Abteilung Strukturforschung, Am Klopferspitz 18a, 82152 Martinsried, Germany

The high precision and fidelity of the genetic message transmission is ensured by numerous proof-reading steps from DNA replication and transcription to protein translation. The key event for translational fidelity is the proper codon assignment for twenty canonical amino acids. An experimental codon reassignment in the genetic code is possible for non-canonical amino acids in vivo using artificially constructed expression hosts submitted to efficient selective pressure. This expansion of an amino acid repertoire in vivo is enabled by the lack of capacity of some of aminoacyl-tRNA synthetases to discriminate between chemically and structurally similar amino acids. Since such non-canonical amino acids may interfere with the cellular metabolism and thus do not belong to the first or restricted part of the universal code but rather to a second or relaxed part which is mainly limited by the downstream proof-reading in the natural translational machinery. On the other hand, not all possible a-amino acids can be introduced into proteins. The aim of our experimental efforts is to determine biological and evolutionary constraints or limits for such in vivo experiments as well as prospects for future development of suitable methodology for in vivo amino acid repertoire extension under the efficient selective pressure. Since aminoacyl-tRNA synthetases are key interpretators of the genetic code, future efforts to break through these limits would certainly include their engineering for relaxed or even novel substrate specificities as well as changes of other protein translation components like tRNAa, in order to generate novel and redundant aminoacylation pathways compatible with the host translational machinery.