In 2010, geneticist Craig Venter unveiled the world’s first synthetic organism — a variant of a bacterium that causes infections in goats. In April, researchers took a step toward a much more useful synthetic microbe, synthesizing from scratch one of the 16 chromosomes of Saccharomyces cerevisiae, or baker’s yeast.
Yeasts, like humans, are eukaryotes: They have complex DNA packaged in chromosomes and riddled with introns (pieces of DNA that don’t contribute to the final protein) and “junk DNA” with no known purpose.
To simplify their task, researchers first searched the computerized genetic code of one chromosome — chromosome 3 — and deleted introns and junk DNA. They added in code to create 98 ready-made cutting sites, like perforations in a sheet of paper, throughout the chromosome. That way, future researchers can pop out various genes and study the effects. Eventually, getting rid of all the non-essential genes would result in a bare-bones yeast with the minimum number of genes possible.
That’s important because yeast is a promising workhorse for synthetic biology. A slimmed-down genome will allow all the cell’s available energy to go toward producing useful chemicals.
The synthetic chromosome, when inserted into a living yeast cell, functioned just like a normal one. That’s good news, but the project to create a fully synthetic yeast genome has a ways to go: Chromosome 3 is just 2.6 percent of the cell’s full genetic code.
But would fully synthetic yeast still be yeast at all? Srinivasan Chandrasegaran, one of the authors of the paper in Science, takes a pragmatic tack: “As long as it tastes like beer, it’s yeast.”
Yeast is already used as a miniature chemical factory in a variety of settings. Custom DNA could make these processes even more efficient.
Artemisinin: Drug manufacturer Sanofi is producing precursors to this anti-malarial drug in genetically modified yeast.
Beer: Brewers today use natural yeasts, but they could eventually design strains to produce exotic beers.
Vaccines: The hepatitis B vaccine is commonly made in modified yeast cells.
Biofuels: Researchers are modifying yeast to produce ethanol and biodiesel.