Xenobiology

from Wikipedia, the free encyclopedia

Xenobiology (XB) is a sub-discipline of synthetic biology that deals with the synthesis and manipulation of complex biological circuits and systems. The prefix comes from the Greek ξένος xénos , German 'guest, stranger' , which indicates that xenobiology describes biological forms that are previously unknown to science or of non-natural origin. In experimental practice, xenobiology refers to novel biological and biochemical systems that differ from the canonical DNA - RNA -20 amino acid system (see Central Dogma of Molecular Biology ). In this sense, in the xenobiology in the natural DNA and RNA molecules, the nucleic bases by non-standard bases replaced ( nucleic acid - analogues ) and / or the sugar ribose (in RNA) or deoxyribose (for DNA) by suitable substituents exchanged ( xenonucleic acids , XNA). Xenobiology also focuses on the expansion of the genetic code and the incorporation of non-proteinogenic amino acids (non-canonical amino acids) into proteins.

Differentiation between xeno-, exo- and astrobiology

The prefix astro (from Greek ἄστρον Astron , German , Star (picture) ' ) as a modifier has the meaning Gestirn-, star, Space , wherein Exo (from Greek ἔξω exo , German , ex = (her) from' ) is assigned as a determinant of the meaning outside, outside . Exobiology and astrobiology deal with the possible existence and formation of extraterrestrial life and the general search for life in space, whereby the interest mostly focuses on planets in the habitable zone . In contrast to astrobiologists who try to detect and analyze possible extraterrestrial life in the universe, xenobiologists are concerned with the attempt to develop life forms with fundamentally different biochemistry or a different genetic code on earth.

Goals of Xenobiology

Xenobiology has the potential to uncover fundamental principles of biology and knowledge about the origin of life . In order to better understand this, it is important to find out why life (most likely) changed from an early RNA world (or an RNA-protein system, also called the ribonucleoprotein world or RNP world ) to today's DNA-RNA- Protein system with a universal genetic code. In this context, the questions are whether life was an evolutionary “coincidence” or whether certain selective compulsions existed that excluded a different biochemistry of life from the beginning. By creating alternative biochemical “ primordial soups ”, it is expected that the fundamental principles that have contributed to the development of life as we know it today will be explored.

Aside from basic research, xenobiology offers numerous new approaches to the development of industrial production systems, with which new manufacturing possibilities in the field of biopolymer engineering and pathogen resistance are created. The genetic code encodes 20 canonical amino acids in all organisms, which are used for protein biosynthesis . In rare cases, the special amino acids selenomethionine , selenocysteine and pyrrolysine are also incorporated into proteins through additional translation components . However, there are 700 other amino acids that are known in biochemistry and whose properties could be used to improve the potential of proteins with regard to more efficient catalytic functions or material properties. The EU-funded METACODE project, for example, aims to establish metathesis - a useful catalytic process previously unknown in living organisms - in bacterial cells. Another potential for the improvement of production processes through xenobiology lies in the possibility of minimizing the risk of virus or bacteriophage infestation during cultivation. Xenobiological cells were no longer suitable as hosts for viruses and phages (bacterial viruses), as they are more resistant to so-called “semantic containment” .

Xenobiology enables the development of novel systems for the containment of genetically modified organisms (biocontainment). The aim is to use a “genetic firewall” to strengthen and diversify current containment approaches. A frequently cited point of criticism of traditional genetic engineering and biotechnology is the possibility of horizontal gene transfer from genetically modified organisms into the environment and the resulting potential risks for nature and human health. One of the main ideas of xenobiology is to develop alternative genetic codes and biochemical building blocks so that horizontal gene transfer is no longer possible. Altered biochemistry would enable new synthetic auxotrophies and use them to create orthogonal biological systems that are no longer compatible with natural genetic systems.

Scientific approach

Xenobiology pursues the goal of constructing and producing biological systems that differ from their natural models on one or more fundamental levels. Ideally, these novel creatures would be different in every possible biochemical aspect and contain a very different genetic code. The long-term goal is to develop a cell that no longer stores its genetic information in DNA and translates it with 20 amino acids, but in alternative information carrier polymers consisting of XNA, alternative base pairing and non-canonical amino acids (i.e. an altered genetic code). So far it has only been possible to create cells that have implemented one or two of the properties mentioned.

Xenonucleic Acids (XNA)

Originally, research into alternative forms of DNA arose from the question of the origin of life and why RNA and DNA were given preference over other possible nucleic acid structures through (chemical) evolution. A systematic investigation aimed at diversifying the chemical structure of nucleic acids resulted in completely new types of information-carrying biopolymers. So far, several XNAs with new chemical backbones or novel nucleobases have been synthesized, for example hexose nucleic acid (HNA), threose nucleic acid (TNA), glycol nucleic acid (GNA) and cyclohexenyl nucleic acid (CeNA). The incorporation of XNA into a plasmid in the form of three HNA codons was already carried out successfully in 2003. These xenonucleic acids are already used in vivo in Escherichia coli as a template for DNA synthesis. A binary genetic cassette (G / T) and two non-DNA bases (Hx / U) were used. While CeNA was also successfully incorporated, every attempt to use GNA as the backbone has failed, since in this case there are too great differences to the natural system to serve as a template for the biosynthesis of DNA by the natural machinery.

Extension of the genetic alphabet

While XNA based on modification in the polymer backbone or to the nucleobases other attempts aim to replace the natural alphabet of DNA or RNA or unnatural base pairs ( English unnatural pair base , UBP) to expand or replace completely (Nukleinsäre analogues) . For example, DNA was produced which instead of the four standard nucleobases (A, T, G and C) contained an extended alphabet with 6 nucleobases (A, T, G, C, dP and dZ). With these two new bases dP stands for 2-amino -8- (1'-β- D -2'-deoxyribofuranosyl) - imidazo [1,2- a ] - 1,3,5-triazine - 4 (8 H ) -one and dZ for 6-amino-5-nitro-3- (1'-β- D -2'-deoxyribofuranosyl) -2 (1 H ) -pyridone. In a systematic study, Leconte et al. the possible incorporation of 60 base candidates (this would correspond to 3600 possible base pairs) in the DNA.

In 2006, a DNA with bases extended by a benzene group or a naphthyl group was examined for the first time (either xDNA or xxDNA or yDNA or yyDNA, depending on the position of the extension groups). However, these extended base pairs, which exist on the chemistry of a natural DNA backbone, could likely be converted back to natural DNA to a limited extent.

Yorke Zhang et al. reported at the turn of the year 2016/2017 on semi-synthetic organisms with a DNA that was expanded to include the bases X (alias NaM) and Y '(alias TPT3) or the nucleotides ( deoxyribonucleotides ) dX (dNaM) and dY' (dTPT3), which pair with each other. This was preceded by experiments with pairings based on the bases X and Y (alias 5SICS), i. H. of nucleotides dX and dY (alias d5SICS).

At the beginning of 2019, there were reports on DNA and RNA with eight bases each (four natural and four synthetic), which are all assigned to each other in pairs ( Hachimoji DNA ).

Novel polymerases

Neither XNA nor the unnatural bases are recognized by natural polymerases . Accordingly, one of the greatest challenges is the development and production of novel types of polymerases that are able to replicate these novel structures. Thus, a modified version has already been HIV - reverse transcriptase discovered was able to produce a Oligonukleotidamplifikat in a PCR amplification containing an additional third base pair. Pinheiro et al. a. (2012) demonstrated that through the evolution and construction of polymerases, genetic information (less than 100 bp in length) can be successfully stored and restored. This was done on the basis of six alternative information storage polymers (xenonucleic acids). Using a modified polymerase, it was also possible to transcribe the Hachimoji DNA into Hachimoji RNA in vitro .

Extension of the genetic code

One of the goals of xenobiology and also of biochemistry is to transform the universal genetic code . Currently, the most promising approach to achieving this goal is to repopulate rare or even unused codons. Ideally, this would create “blanks ” in the current code that can be filled with new, non-canonical amino acids (ncAA) ( “expansion of the genetic code” , code expansion ).

Since such strategies are very difficult to implement and take a long time, short-term shortcuts can also be taken. In “engineering the genetic code” ( code engineering ), for example, bacteria that cannot produce certain amino acids themselves are offered isostructural analogues of natural amino acids under certain culture conditions, which they then incorporate into proteins instead of natural amino acids. With this method, however, only one canonical amino acid is replaced by a non-canonical one and, strictly speaking, there is no “expansion” of the genetic code. In this way, however, it is easily possible to incorporate several non-canonical amino acids into proteins at the same time. However, the amino acid portfolio can not only be expanded, but also reduced. Codon specificity can be changed by modifying new tRNA / aminoacyl-tRNA synthetase pairs to recognize different codons. Cells with such a new configuration are then able to decipher mRNA sequences that would be unusable for the natural protein biosynthetic machinery. Based on this, novel tRNAs / aminoacyl-tRNA synthetase pairs can also be used for the site-specific in vivo incorporation of non-canonical amino acids. In the past, the rearrangement of codons mainly only happened to a very limited extent. In 2013, however, a complete codon was removed from a genome for the first time, which is now free for occupation with new amino acids. Specifically, the groups headed by Farren Isaac and Georg Church at Harvard University were able to replace all 314 TAG stop codons in the genome of E. coli with TAA stop codons, demonstrating that a massive exchange of individual codons by others without fatal effects for the respective organism is possible. Building on this success of the genome-wide codon exchange, the working groups were able to replace 13 codons in 42 essential genes with their synonyms and thus reduce the genetic code in these genes from 64 to 51 codons used.

An even more radical step towards changing the genetic code is the transition away from the natural triplet codons and towards quadruplet or even pentaplet codons. Masahiko Sisido and Schultz did pioneering work in this area, where Sisido managed to establish a pentable code in a cell-free system and Schultz even got bacteria to work with quadruplet codons instead of the usual triplets. Ultimately, it is even possible to use the unnatural nucleobases mentioned above to introduce non-canonical amino acids into proteins. In 2017 Escherichia coli were published that can use six nucleotides instead of the usual four.

Directed evolution

Another possibility to replace DNA with XNA would be to change the cell environment in a targeted manner instead of the genetic molecules. This approach has already been successfully demonstrated by Marliere and Mutzel by creating a new E. coli strain that has a DNA structure composed of the standard nucleotides A, C and G as well as a synthetic thymine analog. The thymine analog 5- chlorouracil was incorporated into the genome in a sequence-specific manner at all positions of the natural thymine. In order to grow, these cells depend on the external addition of the base 5-chlororacil, but otherwise behave like normal coli bacteria. This approach creates two levels of protection to prevent any interaction between unnatural and natural bacteria, as the strain possesses an auxotrophy for an unnatural chemical substance and the organism also has a DNA form that cannot be deciphered by any other organism.

Biological safety

Xenobiological systems were designed to be orthogonal to the natural biological systems of our planet. An (but so far purely hypothetical) XNA organism that has XNA, other base pairs and new polymerases and uses an altered genetic code will find it very difficult to interact with the natural forms of life at the genetic level. In this sense, xenobiological organisms represented a genetic enclave that cannot exchange genetic information with natural cells. The change in the genetic replication machine of a cell therefore leads to a so-called "semantic containment". As a security concept, this - in analogy to information processing in the IT area - can be referred to as a genetic firewall. This concept of a genetic firewall appears to address several limitations in existing biological security systems. The first experimental evidence showing the theoretical concept of the genetic firewall as an effective future instrument was provided in 2013 with the creation of a genome-recoded organism (GRO). In this organism, all TAG stop codons in E. coli have been replaced by TAA codons. This enabled the deletion of the release factor RF 1 and, based on this, the replacement of the TAG codon, which was converted from the stop signal to the amino acid codon. This GRO subsequently showed a higher resistance to T7 bacteriophage infections. This underlines that alternative genetic codes can reduce genetic compatibility. Nevertheless, this GRO is still very similar to its natural predecessors and therefore does not yet have a “genetic firewall”. The example shows, however, that the repopulation of a larger number of triplet codons opens up the prospect of generating bacterial strains that use XNA, new base pairs, new genetic codes, and so on in the not so distant future. With these semantic changes, these tribes would then no longer be able to exchange genetic information with the natural environment. While such a genetic firewall would implement semantic containment mechanisms in new organisms, new biochemical systems for toxins and xenobiotics also have yet to be developed.

Legal framework, regulation

Xenobiology could break the current regulatory framework and lead to new legal challenges. Currently, laws and guidelines deal with genetically modified organisms (GMOs), but in no way mention chemically modified or genome-recoded organisms. Given that real xenobiological organisms are not yet to be expected in the next few years, decision makers still have time to prepare for future regulatory challenges. Since 2012 there have been corresponding political advisors in the USA, four national committees for biosafety in Europe, the European Molecular Biology Organization, and the Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR) of the European Commission in three opinions (definition, risk assessment methodologies and safety aspects, and Risks to the environment and biodiversity related to synthetic biology and research priorities in the field of synthetic biology) in order to deal with this topic as a field to be regulated in the future.

See also

literature

  • Markus Schmidt et al. : Xenobiology: State-of-the-Art, Ethics, and Philosophy of New-to-Nature Organisms in: Huimin Zhao et al. : Synthetic Biology - Metabolic Engineering , Springer, Cham 2017, ISBN 978-3-319-55317-7 .

Web links

Individual evidence

  1. ^ A b Vitor B. Pinheiro, Philipp Holliger: The XNA world: progress towards replication and evolution of synthetic genetic polymers . In: Current Opinion in Chemical Biology . tape 16 , no. 3–4 , August 2012, pp. 245-252 , doi : 10.1016 / j.cbpa.2012.05.198 .
  2. ↑ JD Bain, Christopher Switzer, Richard Chamberlin, Steven A. Bennert: Ribosome-mediated incorporation of a non-standard amino acid into a peptide through expansion of the genetic code . In: Nature . tape 356 , no. 6369 , April 9, 1992, pp. 537-539 , doi : 10.1038 / 356537a0 .
  3. ↑ CJ Noren, SJ Anthony-Cahill, MC Griffith, PG Schultz: A general method for site-specific incorporation of unnatural amino acids into proteins . In: Science . tape 244 , no. 4901 , April 14, 1989, p. 182-188 , doi : 10.1126 / science.2649980 , PMID 2649980 .
  4. ↑ Duden: Astro
  5. ↑ Duden: Exo
  6. ↑ a b Markus Schmidt: Xenobiology: A new form of life as the ultimate biosafety tool . In: BioEssays . tape 32 , no. 4 , 2010, p. 322–331 , doi : 10.1002 / bies.200900147 .
  7. ↑ Norman R. Pace: The universal nature of biochemistry . In: Proceedings of the National Academy of Sciences . tape 98 , no. 3 , January 30, 2001, p. 805-808 , doi : 10.1073 / pnas.98.3.805 , PMID 11158550 .
  8. ↑ Birgit Wiltschi, Nediljko Budisa : Natural history and experimental evolution of the genetic code . In: Applied Microbiology and Biotechnology . tape 74 , no. 4 , March 1, 2007, p. 739-753 , doi : 10.1007 / s00253-006-0823-6 .
  9. ↑ V. Kubyshkin, CG Acevedo-Rocha, N. Budisa: On universal coding events in protein biogenesis . In: Biosystems . 2017. doi : 10.1016 / j.biosystems.2017.10.004 .
  10. ↑ a b Piet Herdewijn, Philippe Marlière: Toward Safe genetically modified organisms through the Chemical Diversification of Nucleic Acids . In: Chemistry & Biodiversity . tape 6 , no. 6 , 2009, p. 791-808 , doi : 10.1002 / cbdv.200900083 .
  11. ↑ V. Kubyshkin, N. Budisa: Synthetic alienation of microbial organisms by using genetic code engineering: Why and how? . In: Biotechnology Journal . 12, 2017, p. 1600097. doi : 10.1002 / biot.201600097 .
  12. ^ Albert Eschenmoser: Chemical Etiology of Nucleic Acid Structure . In: Science . tape 284 , no. 5423 , June 25, 1999, p. 2118-2124 , doi : 10.1126 / science.284.5423.2118 , PMID 10381870 .
  13. ↑ Karen Vastmans, Matheus Froeyen, Luc Kerremans, Sylvie Pochet, Piet Herdewijn: Reverse transcriptase incorporation of 1,5-anhydrohexitol nucleotides . In: Nucleic Acids Research . tape 29 , no. 15 , January 8, 2001, p. 3154-3163 , doi : 10.1093 / nar / 29.15.3154 , PMID 11470872 .
  14. ↑ Mi-Yeon Jang et al .: A Synthetic Substrate of DNA Polymerase Deviating from the Bases, Sugar, and Leaving Group of Canonical Deoxynucleoside Triphosphates . In: Chemistry & Biology . tape 20 , no. 3 , March 21, 2013, p. 416-423 , doi : 10.1016 / j.chembiol.2013.02.010 .
  15. ^ Vitor B. Pinheiro, David Loakes, Philipp Holliger: Synthetic polymers and their potential as genetic materials . In: BioEssays . tape 35 , no. 2 , 2013, p. 113-122 , doi : 10.1002 / bies.201200135 .
  16. ↑ Justin K. Ichida, Allen Horhota, Keyong Zou, Larry W. McLaughlin, Jack W. Szostak: High fidelity TNA synthesis by Therminator polymerase . In: Nucleic Acids Research . tape 33 , no. 16 , January 1, 2005, p. 5219-5225 , doi : 10.1093 / nar / gki840 , PMID 16157867 .
  17. ↑ Veerle Kempeneers, Marleen Renders, Matheus Froeyen, Piet Herdewijn: Investigation of the DNA-dependent cyclohexenyl nucleic acid polymerization and the cyclohexenyl nucleic acid-dependent DNA polymerization . In: Nucleic Acids Research . tape 33 , no. 12 , January 1, 2005, p. 3828-3836 , doi : 10.1093 / nar / gki695 , PMID 16027107 .
  18. ↑ Sylvie Pochet, P. Alexandre Kaminski, Arthur Van Aerschot, Piet Herdewijn, Philippe Marlière: Replication of hexitol oligonucleotides as a prelude to the propagation of a third type of nucleic acid in vivo . In: Comptes Rendus Biologies . tape 326 , no. December 12 , 2003, p. 1175-1184 , doi : 10.1016 / j.crvi.2003.10.004 .
  19. ↑ Valérie Pezo, Feng Wu Liu, Mikhail Abramov, Mathy Froeyen, Piet Herdewijn, Philippe Marlière: Binary Genetic Cassettes for Selecting XNA-Templated DNA Synthesis In Vivo . In: Angewandte Chemie International Edition . tape 52 , no. 31 , 2013, p. 8139-8143 , doi : 10.1002 / anie.201303288 .
  20. ↑ Kyung Hyun Lee, Kiyofumi Hamashima, Michiko Kimoto, Ichiro Hirao: Genetic alphabet expansion biotechnology by creating unnatural base pairs, in: Current Opinion in Biotechnology, Volume 51, June 2018, pp. 8-15, ScienceDirect , ResearchGate , PubMed , doi : 10.1016 / j.copbio
  21. ↑ AM Sismour, S. Lutz, JH Park, MJ Lutz, PL Boyer, SH Hughes, SA Benner: PCR amplification of DNA containing non-standard base pairs by variants of reverse transcriptase from Human Immunodeficiency Virus-1. In: Nucleic acids research . Volume 32, number 2, 2004, pp. 728-735, doi: 10.1093 / nar / gkh241 , PMID 14757837 , PMC 373358 (free full text).
  22. ↑ Z. Yang, D. Hutter, P. Sheng, AM Sismour and SA Benner: Artificially expanded genetic information system: a new base pair with an alternative hydrogen bonding pattern. (2006) Nucleic Acids Res. 34, pp. 6095-6101. PMC 1635279 (free full text)
  23. ↑ Z. Yang, AM Sismour, P. Sheng, NL Puskar, SA Benner: Enzymatic incorporation of a third nucleobase pair. In: Nucleic acids research . Volume 35, No. 13, 2007, pp. 4238-4249, doi: 10.1093 / nar / gkm395 , PMID 17576683 , PMC 1934989 (free full text).
  24. ↑ Aaron M. Leconte, Gil Tae Hwang, Shigeo Matsuda, Petr Capek, Yoshiyuki Hari, Floyd E. Romesberg: Discovery, Characterization, and Optimization of an Unnatural Base Pair for Expansion of the Genetic Alphabet . In: Journal of the American Chemical Society . tape 130 , no. 7 , February 2008, p. 2336-2343 , doi : 10.1021 / ja078223d , PMID 18217762 , PMC 2892755 (free full text).
  25. ^ SR Lynch, H. Liu, J. Gao, ET Kool: Toward a designed, functioning genetic system with expanded-size base pairs: solution structure of the eight-base xDNA double helix. In: Journal of the American Chemical Society. Volume 128, No. 45, November 2006, pp. 14704-14711, doi: 10.1021 / ja065606n . PMID 17090058 . PMC 2519095 (free full text).
  26. ↑ Andrew T. Krueger, Larryn W. Peterson, Jijumon Chelliserry, Daniel J. Kleinbaum, Eric T. Kool: Encoding Phenotype in Bacteria with an Alternative Genetic Set . In: Journal of the American Chemical Society . tape 133 , no. 45 , November 16, 2011, p. 18447-18451 , doi : 10.1021 / ja208025e .
  27. ↑ Yorke Zhang, Brian M. Lamb, Aaron W. Feldman, Anne Xiaozhou Zhou, Thomas Lavergne, Lingjun Li, Floyd E. Romesberg: A semisynthetic organism engineered for the stable expansion of the genetic alphabet , in: PNAS February 7, 2017, 114 (6), pp. 1317-1322; first published January 23, 2017, doi: 10.1073 / pnas.1616443114 , Ed .: Clyde A. Hutchison III, The J. Craig Venter Institute
  28. ↑ scinexx: Researchers breed "Frankenstein" microbe , from January 24, 2017
  29. ↑ a b Shuichi Hoshika, Nicole A. Leal, Myong-Jung Kim, Myong-Sang Kim, Nilesh B. Karalkar, Hyo-Joong Kim, Alison M. Bates, Norman E. Watkins Jr., Holly A. SantaLucia, Adam J. Meyer, Saurja DasGupta, Joseph A. Piccirilli, Andrew D. Ellington, John Santa Lucia Jr., Millie M. Georgiadis, Steven A. Benner: Hachimoji DNA and RNA: A genetic system with eight building blocks. Science 363 (6429) February 22, 2019; Pp. 884-887. doi : 10.1126 / science.aat0971 .
  30. ↑ A. Michael Sismour, Steven A. Benner: The use of thymidine analogs to improve the replication of an extra DNA base pair: a synthetic biological system . In: Nucleic Acids Research . tape 33 , no. 17 , 2005, pp. 5640–5646 , doi : 10.1093 / nar / gki873 , PMID 16192575 , PMC 1236980 (free full text).
  31. ↑ Stephanie A. Havemann, Shuichi Hoshika, Daniel Hutter, Steven A. Benner: Incorporation of Multiple Sequential Pseudothymidines by DNA Polymerases and Their Impact on DNA Duplex Structure . In: Nucleosides, Nucleotides and Nucleic Acids . tape 27 , no. 3 , February 2008, p. 261-278 , doi : 10.1080 / 15257770701853679 , PMID 18260010 .
  32. Jump up ↑ Vitor B. Pinheiro, Alexander I. Taylor, Christopher Cozens, Mikhail Abramov, Marleen Renders, Su Zhang, John C. Chaput, Jesper Wengel, Sew-Yeu Peak-Chew, Stephen H. McLaughlin, Piet Herdewijn, Philipp Holliger: Synthetic genetic polymers capable of heredity and evolution . In: Science . tape 336 , no. 6079 , April 2012, p. 341-344 , doi : 10.1126 / science.1217622 , PMID 22517858 , PMC 3362463 (free full text).
  33. ↑ Y. Fan, CR Evans, J. Ling: Rewiring protein synthesis: From natural to synthetic amino acids. In: Biochimica et Biophysica Acta . Volume 1861, number 11 Pt B, 11 2017, pp. 3024–3029, doi : 10.1016 / j.bbagen.2017.01.014 , PMID 28095316 , PMC 5511583 (free full text).
  34. ↑ Nediljko Budisa: Engineering the genetic code: expanding the amino acid repertoire for the design of novel proteins . Wiley-VCH, Weinheim 2005, ISBN 3-527-31243-9 .
  35. ↑ Michael Georg Hoesl, Nediljko Budisa: Recent advances in genetic code engineering in Escherichia coli . In: Current Opinion in Biotechnology . tape 23 , no. 5 , October 2012, p. 751-757 , doi : 10.1016 / j.copbio.2011.12.027 , PMID 22237016 .
  36. ↑ V. Pezo include: A Metabolic Prototype for Eliminating tryptophan From The Genetic Code . In: Scientific Reports . tape 3 , February 28, 2013, doi : 10.1038 / srep01359 .
  37. ↑ Oliver Rackham, Jason W. Chin: A network of orthogonal ribosome mRNA pairs . In: Nature Chemical Biology . tape 1 , no. 3 , August 2005, p. 159-166 , doi : 10.1038 / nchembio719 .
  38. ^ Lei Wang, Ansgar Brock, Brad Herberich, Peter G. Schultz: Expanding the Genetic Code of Escherichia coli . In: Science . tape 292 , no. 5516 , April 20, 2001, p. 498-500 , doi : 10.1126 / science.1060077 , PMID 11313494 .
  39. ^ Matthew CT Hartman, Kristopher Josephson, Chi-Wang Lin, Jack W. Szostak: An Expanded Set of Amino Acid Analogs for the Ribosomal Translation of Unnatural Peptides . In: PLoS ONE . tape 2 , no. 10 , October 3, 2007, p. e972 , doi : 10.1371 / journal.pone.0000972 .
  40. ^ Farren J. Isaacs et al: Precise Manipulation of Chromosomes in Vivo Enables Genome-Wide Codon Replacement . In: Science . tape 333 , no. 6040 , July 15, 2011, p. 348-353 , doi : 10.1126 / science.1205822 , PMID 21764749 .
  41. ↑ MJ Lajoie, S. Kosuri, JA Mosberg, CJ Gregg, D. Zhang, GM Church: Probing the Limits of Genetic Recoding in Essential Genes . In: Science . tape 342 , no. 6156 , October 18, 2013, p. 361-363 , doi : 10.1126 / science.1241460 , PMID 24136967 .
  42. ↑ Takahiro Hohsaka, Masahiko Sisido: Incorporation of non-natural amino acids into proteins . In: Current Opinion in Chemical Biology . tape 6 , no. 6 , December 1, 2002, pp. 809-815 , doi : 10.1016 / S1367-5931 (02) 00376-9 .
  43. ↑ J. Christopher Anderson, Ning Wu, Stephen W. Santoro, Vishva Lakshman, David S. King, Peter G. Schultz: An expanded genetic code with a functional quadruplet codon . In: Proceedings of the National Academy of Sciences . tape 101 , no. 20 , May 18, 2004, p. 7566-7571 , doi : 10.1073 / pnas.0401517101 , PMID 15138302 .
  44. ↑ Ichiro Hirao et al: An unnatural base pair for incorporating amino acid analogs into proteins . In: Nature Biotechnology . tape 20 , no. 2 , February 2002, p. 177-182 , doi : 10.1038 / nbt0202-177 .
  45. ↑ Yorke Zhang, Brian M. Lamb, Aaron W. Feldman, Anne Xiaozhou Zhou, Thomas Lavergne, Lingjun Li, Floyd E. Romesberg: A semisynthetic organism engineered for the stable expansion of the genetic alphabet. In: Proceedings of the National Academy of Sciences. , S. 201616443, doi: 10.1073 / pnas.1616443114 .
  46. ^ Philippe Marlière et al: Chemical Evolution of a Bacterium's Genome . In: Angewandte Chemie International Edition . tape 50 , no. 31 , 2011, p. 7109–7114 , doi : 10.1002 / anie.201100535 .
  47. ↑ Philippe Marliere: The farther, the safer: a manifesto for securely navigating synthetic species away from the old living world . In: Systems and Synthetic Biology . tape 3 , no. 1–4 , December 1, 2009, pp. 77-84 , doi : 10.1007 / s11693-009-9040-9 .
  48. ^ Carlos G. Acevedo-Rocha, Nediljko Budisa: On the Road towards Chemically Modified Organisms Endowed with a Genetic Firewall . In: Angewandte Chemie International Edition . tape 50 , no. 31 , 2011, p. 6960–6962 , doi : 10.1002 / anie.201103010 .
  49. ↑ Gerd HG Moe-Behrens, Rene Davis, Karmella A. Haynes: Preparing synthetic biology for the world . In: Frontiers in Microbiotechnology, Ecotoxicology and Bioremediation . tape 4 , 2013, p. 5 , doi : 10.3389 / fmicb.2013.00005 .
  50. ↑ Oliver Wright, Guy-Bart Stan, Tom Ellis: Building-in Biosafety for Synthetic Biology . In: Microbiology . March 21, 2013, p. 1221-1350 , doi : 10.1099 / mic.0.066308-0 , PMID 23519158 .
  51. ↑ Marc J. Lajoie et al. a .: Genomically Recoded Organisms Expand Biological Functions . In: Science . tape 342 , no. 6156 , October 18, 2013, p. 357-360 , doi : 10.1126 / science.1241459 , PMID 24136966 .
  52. ^ Markus Schmidt, Lei Pei: Synthetic Toxicology: Where Engineering Meets Biology and Toxicology . In: Toxicological Sciences . tape 120 , Suppl. 1, January 3, 2011, p. S204-S224 , doi : 10.1093 / toxsci / kfq339 , PMID 21068213 .
  53. ↑ a b Markus Schmidt: 21st Century Borders / Synthetic Biology: Focus on Responsibility and Governance . Institute on Science for Global Policy (ISGP), Tucson, Arizona 2012, ISBN 978-0-9803882-4-0  ( formally incorrect ) , chapter Safeguarding the Genetic Firewall with Xenobiology ( scienceforglobalpolicy.org [PDF]).
  54. ↑ K. Pauwels et al: Event report: SynBio Workshop (Paris 2012) - Risk assessment challenges of Synthetic Biology. (2013) Journal for Consumer Protection and Food Safety. doi: 10.1007 / s00003-013-0829-9
  55. ↑ M. Garfinkel: Biological containment of synthetic microorganisms: science and policy. (2013) Report on an ESF / LESC Strategic Workshop.
  56. ↑ Vermeire T. et al. 2014. Final Opinion on Synthetic Biology: Definition . Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR)
  57. ↑ Vermeire T. et al. 2015. Final Opinion on Synthetic Biology II: Risk assessment methodologies and safety aspects. Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR)
  58. ↑ Vermeire T. et al. 2015. Final Opinion on Synthetic Biology III: Risks to the environment and biodiversity related to synthetic biology and research priorities in the field of synthetic biology. Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR)
  59. ↑ Valérie Pezo: Xenome , Institute of Systems & Synthetic Biology
  60. ↑ B. Bauwens: Molecular evolution of polymerases for the synthesis of deoxyxylose-based nucleic acids , 2018 © KU Leuven