Both exo- and astrobiology deal with the search for naturally evolved life in the Universe, mostly on other planets in the circumstellar habitable zone.
[2] In xenobiology, the aim is to design and construct biological systems that differ from their natural counterparts on one or more fundamental levels.
[15] Systematic experimental studies aiming at the diversification of the chemical structure of nucleic acids have resulted in completely novel informational biopolymers.
This study, using a binary (G/T) genetic cassette and two non-DNA bases (Hx/U), was extended to CeNA, while GNA seems to be too alien at this moment for the natural biological system to be used as template for DNA synthesis.
While XNAs have modified backbones, other experiments target the replacement or enlargement of the genetic alphabet of DNA with unnatural base pairs.
[27] In 2002, Hirao et al. developed an unnatural base pair between 2-amino-8-(2-thienyl)purine (s) and pyridine-2-one (y) that functions in vitro in transcription and translation toward a genetic code for protein synthesis containing a non-standard amino acid.
In one case a modified variant of the HIV-reverse transcriptase was found to be able to PCR-amplify an oligonucleotide containing a third type base pair.
[36][37] Pinheiro et al. (2012) demonstrated that the method of polymerase evolution and design successfully led to the storage and recovery of genetic information (of less than 100bp length) from six alternative genetic polymers based on simple nucleic acid architectures not found in nature, xeno nucleic acids.
Cells endowed with such aminoacyl-[tRNA synthetases] are thus able to read [mRNA] sequences that make no sense to the existing gene expression machinery.
[42] Altering the codon: tRNA synthetases pairs may lead to the in vivo incorporation of the non-canonical amino acids into proteins.
[54][55] A first experimental evidence of the theoretical concept of the genetic firewall was achieved in 2013 with the construction of a genomically recoded organism (GRO).
The possibility of reassigning the function of large number of triplets opens the perspective to have strains that combine XNA, novel base pairs, new genetic codes, etc.
Regardless of changes leading to a semantic containment mechanism in new organisms, any novel biochemical systems still has to undergo a toxicological screening.
Taking into account that real xenobiology organisms are not expected in the next few years, policy makers do have some time at hand to prepare themselves for an upcoming governance challenge.
Since 2012, the following groups have picked up the topic as a developing governance issue: policy advisers in the US,[59] four National Biosafety Boards in Europe,[60] the European Molecular Biology Organisation,[61] and the European Commission's Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR) in three opinions (Definition,[62] risk assessment methodologies and safety aspects,[63] and risks to the environment and biodiversity related to synthetic biology and research priorities in the field of synthetic biology.