<p> In a breakthrough, scientists have created the first stable semi-synthetic organism - a single-celled bacterium - that may play important roles in drug discovery and other applications.<br /><br /></p>.<p>Life's genetic code has only ever contained four natural bases. These bases pair up to form two base pairs - the rungs of the DNA ladder - and they have simply been rearranged to create all life as we know it, from bacteria to humans.<br /><br />Building on earlier research in which they synthesised a DNA base pair, scientists at The Scripps Research Institute (TSRI) in the US created a new bacterium that uses the four natural bases (called A, T, C and G), which every living organism possesses, but that also holds as a pair two synthetic bases called X and Y in its genetic code.<br />Researchers have now shown that the single-celled organism can hold on to the synthetic base pair as it divides.<br /><br />"We've made this semi-synthetic organism more life-like," said Floyd Romesberg, professor at TSRI.<br /><br />Researchers said the work could be used to create new functions for single-celled organisms that play important roles in drug discovery and much more.<br /><br />They had earlier showed that E coli bacteria could hold a synthetic base pair in their genetic code. However, they could not keep the base pair in their code indefinitely as they divided.<br /><br />The X and Y base pair was dropped over time, limiting the ways the organism could use the additional information possessed in their DNA.<br /><br />"If the semi-synthetic organism is going to really be an organism, it has to be able to stably maintain that information," said Romesberg.<br /><br />Researchers developed the means for the single-celled organism to retain the artificial base pair.<br /><br />They optimised a tool called a nucleotide transporter, which brings the materials necessary for the unnatural base pair to be copied across the cell membrane.<br /><br />The researchers discovered a modification to the transporter that that made it much easier for the organism to grow and divide while holding on to X and Y.<br /><br />They then optimised their previous version of Y, creating a chemically different molecule that can be better recognised by the enzymes that synthesise DNA molecules during DNA replication. This made it easier for cells to copy the synthetic base pair.<br /><br />Researchers then used gene editing tool CRISPR-Cas9 to design their organism to see a genetic sequence without X and Y as a foreign invader.<br /><br />A cell that dropped X and Y would be marked for destruction, leaving the scientists with an organism that could hold on to the new bases.<br /><br />Their semi-synthetic organism was thus able to keep X and Y in its genome after dividing 60 times, leading the researchers to believe it can hold on to the base pair indefinitely.The research was published in the journal PNAS.</p>
<p> In a breakthrough, scientists have created the first stable semi-synthetic organism - a single-celled bacterium - that may play important roles in drug discovery and other applications.<br /><br /></p>.<p>Life's genetic code has only ever contained four natural bases. These bases pair up to form two base pairs - the rungs of the DNA ladder - and they have simply been rearranged to create all life as we know it, from bacteria to humans.<br /><br />Building on earlier research in which they synthesised a DNA base pair, scientists at The Scripps Research Institute (TSRI) in the US created a new bacterium that uses the four natural bases (called A, T, C and G), which every living organism possesses, but that also holds as a pair two synthetic bases called X and Y in its genetic code.<br />Researchers have now shown that the single-celled organism can hold on to the synthetic base pair as it divides.<br /><br />"We've made this semi-synthetic organism more life-like," said Floyd Romesberg, professor at TSRI.<br /><br />Researchers said the work could be used to create new functions for single-celled organisms that play important roles in drug discovery and much more.<br /><br />They had earlier showed that E coli bacteria could hold a synthetic base pair in their genetic code. However, they could not keep the base pair in their code indefinitely as they divided.<br /><br />The X and Y base pair was dropped over time, limiting the ways the organism could use the additional information possessed in their DNA.<br /><br />"If the semi-synthetic organism is going to really be an organism, it has to be able to stably maintain that information," said Romesberg.<br /><br />Researchers developed the means for the single-celled organism to retain the artificial base pair.<br /><br />They optimised a tool called a nucleotide transporter, which brings the materials necessary for the unnatural base pair to be copied across the cell membrane.<br /><br />The researchers discovered a modification to the transporter that that made it much easier for the organism to grow and divide while holding on to X and Y.<br /><br />They then optimised their previous version of Y, creating a chemically different molecule that can be better recognised by the enzymes that synthesise DNA molecules during DNA replication. This made it easier for cells to copy the synthetic base pair.<br /><br />Researchers then used gene editing tool CRISPR-Cas9 to design their organism to see a genetic sequence without X and Y as a foreign invader.<br /><br />A cell that dropped X and Y would be marked for destruction, leaving the scientists with an organism that could hold on to the new bases.<br /><br />Their semi-synthetic organism was thus able to keep X and Y in its genome after dividing 60 times, leading the researchers to believe it can hold on to the base pair indefinitely.The research was published in the journal PNAS.</p>