A landmark step towards the creation of artificial life has been taken by scientists who have built a functioning synthetic yeast chromosome.

Their achievement breaks new ground by taking the emerging field of synthetic biology beyond the limits of bacteria and viruses.

Synthetic strains of yeast could be used in the manufacture of medicines or vaccines or bolster the development of efficient biofuels, the scientists claim.

Chromosomes are tiny packages of DNA that contain the genes in which the ‘book of life’ is written.

Previously scientists have built artificial versions of bacterial chromosomes, as well as viral DNA. But this is the first time the chromosome of a ‘eukaryote’ – a higher organism whose cells contain nuclei, unlike bacteria – has been created.

US synthetic biology pioneer Jef Boeke, director of the New York University Langone Medical Centre, said: “Our research moves the needle in synthetic biology from theory to reality.

“This work represents the biggest step yet in an international effort to construct the full genome of synthetic yeast.”

Writing in the journal Science, the team describes how the chromosome – dubbed synIII – was constructed and successfully incorporated into brewer’s yeast. The seven-year-long project involved piecing together some 273,871 DNA components. The scientists also tweaked nature’s design by removing repeated DNA sections thought to be unnecess-ary to reproduction and growth.

Regions of ‘junk’ DNA that appeared to perform no function were taken out, as well as ‘jumping gene’ segments known to move around randomly and introduce mutations.

Synthetic strains of yeast could be used in the manufacture of medicines or vaccines or bolster the development of efficient biofuels

“When you change the genome you’re gambling,” said Boeke. “One wrong change can kill the cell.

“We have made over 50,000 changes to the DNA code in the chromosome and our yeast still lives. That is remarkable. It shows that our synthetic chromosome is hardy, and it endows the yeast with new properties.”

Sixty undergraduate students were recruited to tie together short snippets of the synthetic DNA into stretches 750 to 1,000 units long.

The research has sparked an ongoing international mission to reconstruct the entire genome of yeast.

Yeast chromosome III was chosen for synthesis because it is among the smallest of the 16 yeast chromosomes. It controls how yeast cells ‘mate’ and undergo genetic change. The organism shares roughly a third of its 6,000 genes – stretches of DNA that encode for proteins – with humans.

Large sections of yeast DNA were manipulated by the scientists using a ‘scrambling’ technique that involves shuffling genes like a deck of cards. “We can pull together any group of cards, shuffle the order and make millions and millions of different decks, all in one small tube of yeast,” Boeke added.

“Now that we can shuffle the genomic deck, it will allow us to ask if we can make a deck of cards with a better hand for making yeast survive under any of a multitude of conditions, such as tolerating higher alcohol levels.”

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