In March undergraduate students in Johns Hopkins University's Build a Genome course announced they had made a yeast chromosome from scratch—and history, too. It is the first time anyone has synthesized the chromosome of a complex organism, a landmark achievement in the field of synthetic biology. It is also a triumph for the movement known as DIY biology.
The target was chromosome 3, which controls the yeast's sexual reproduction and has 316,617 base pairs of the DNA alphabet—A for adenine, G for guanine, C for cytosine and T for thymine. To synthesize it, the students took a shortcut: they built only the sections considered essential or nonrepetitive. The resulting chromosome had a more manageable 272,871 base pairs. And as reported in Science, the yeast with the new genes thrived just as well as regular yeast did in terms of size and growth.
“They are going strong,” says biologist Jef Boeke of New York University, who helped lead the research as part of the Synthetic Yeast 2.0 project—an effort to build a synthetic genome for yeast that would give scientists nearly complete control of it. Boeke and others plan to grow this batch for thousands of generations over the next several years to see how they evolve over time, which will give scientists a better understanding of fundamental biology, from the role of “junk DNA” to the absolute minimum of genetic code necessary for survival. “The questions are endless,” Boeke says.
The current work is just 3 percent of the way toward creating an entirely synthetic yeast genome (there are 16 chromosomes in total) and will take many more years to finish. If finished, synthetic yeast could be second on the list of organisms with genomes built from scratch—the J. Craig Venter Institute built a bacterium's genome in 2010.
It could also be a breakthrough in humanity's millennia-long cohabitation with Saccharomyces cerevisiae, which is responsible for bread and wine. Yeasts today churn out human proteins for medicines, biofuels and other specialty products. Being able to fine-tune the microscopic fungus's genetics could lead to better beer or sustainable chemicals, according to Boeke. And after yeast? “The fruit fly? The worm? We're not sure what is next.”