Yeast is already invaluable to humans - it helps make beer and bread - but scientists are hoping to use it to mass produce lifesaving drugs.
The technique could boost the drug industry
US researchers have managed to get a particular type of yeast to secrete a body chemical called a glycoprotein.
This and similar proteins are the raw materials in many modern drugs, but making them is currently costly and labour-intensive.
The method, described in the journal Science, may lead to cheaper drugs.
Glycoproteins have a sugar coating which is key to the way they behave once they are in the body.
The researchers, from Dartmouth College in New Hampshire, subtly changed the DNA of the yeast Pichia pastoris so that they produced human versions of these chemicals.
The yeast seems able to produce glycoproteins which are uniform - a potential godsend for the pharmaceutical industry.
In theory, patients with a wide variety of conditions - from cancer to haemophilia, could benefit.
Proteins such as these need to be made by living cells, and at present, the only way of making them are to culture them in mammal cells, for example hamster cells, in a laboratory.
This is a painstaking process, and the proteins cannot be produced in large batches.
The arrival of the modified yeast removes restrictions on mass production.
Dr Tillman Gerngross, who led the research: "For the first time, we have shown that yeast an be used to produce a complex human glycoprotein.
"This technology has the potential to revolutionise the way therapeutic proteins are made - better, cheaper, faster, safer - and offer a level of control over the quality of the end product that has never existed before."
Charles Hutchinson, the chief executive of GlycoFi, the company behind the research, said: "This development is very timely considering the production capacity bottleneck that's facing today's biomanufacturing industry."