When Stan Fields was a boy, he collected articles from newspapers and magazines about new medical discoveries and technologies. He also loved puzzles. Those interests spurred him to study biology in college. As an undergraduate in Middlebury College, he performed research on an unusual genetic phenomenon in wasps and enjoyed trying to solve nature's enigmas.
As a graduate student in the late 1970s at the Medical Research Council Laboratory of Molecular Biology in Cambridge, England, Fields was inspired by Fred Sanger, one of his mentors. Sanger had just developed a new method to sequence DNA, which would win him a second Nobel Prize in 1980, and ultimately revolutionize biomedical research. Sequencing enabled a fundamental understanding of the blueprint of life encoded in the chromosomes of all organisms, from viruses to humans.
Fields, who analyzed the genome of an influenza virus for his doctoral research, was one of the first scientists in the world to use Sanger's new technique.
Seeing the power of a technology, such as DNA sequencing, to transform biologists' understanding of nature had a huge impact on Fields. In 1987, as an assistant professor at the State University of New York at Stony Brook, he too invented a technique, called the yeast two-hybrid system, that also irrevocably transformed biology.
The method, whose application throughout the world of biology began in the late 1990s, allows scientists to more easily study which proteins in the cell interact with which other ones.
Proteins, which are essential to life, don't work in isolation. They form living machines, complexes of dozens of proteins that fit together like a jigsaw puzzle, Fields explained. To see the whole picture, scientists need to identify which pieces, or proteins, fit next to or interact directly with each other.
The two-hybrid system uses the interior workings of yeast to find among thousands of jumbled puzzle pieces, or the proteins in any cell, those that bind each other. Essentially, Fields said, the method biochemically rigs each protein puzzle piece so that if it binds its partner, a circuit is completed, and a light bulb goes off.
The light represents expression of a yeast reporter gene. The rigging involves splitting in two a protein, called a transcription factor, that regulates the reporter gene's expression, with each piece joined to a test protein. Only when the two fused test proteins—which normally interact in their cellular milieu—find each other in the yeast artificial system do they bring back together the two pieces of the transcription factor. This rejoining reconstitutes the factor's activity and results in expression of the reporter gene.
Before Fields invented his method, scientists had to use time-consuming biochemical techniques to isolate proteins and those with which they bind.
Initially, scientists used the two-hybrid method to find partners of single yeast proteins, and then soon after, to find partners of single proteins found in cells from many other organisms, including humans, bacteria, and fruit flies. Now, with robotics and automated procedures and sequence data from the many different genome projects, they can analyze protein interactions at an enormous scale—thousands of proteins can be screened for partners in a single set of experiments.
With knowledge of two binding partners from the method, scientists in disciplines from neuroscience, to cancer research, to cell biology have been able to construct complex biological networks that include thousands of proteins, in both normal and diseased states. Newer techniques, such as proteomics based on mass spectrometry, also allow identification of protein interactions, adding to what Fields helped start.
Fields is gratified the two-hybrid system changed biomedical science. Today, though, only a small part of his laboratory continues to adapt the technology. Most of his group's research involves developing other new approaches—which he acknowledges don't always work—to study the activities of proteins and other biomolecules.
His laboratory is trying, for example, to find proteins in the cell that tag others for destruction. Some lab members are also attempting to develop a system to manufacture small pieces of thousands of different proteins as a possible way to screen for new drugs. Others are analyzing small molecules—such as amino acids—on a high-throughput basis.
"Technology development is the most purely creative aspect of science," he said. "You can sit down and envision some kind of method or device that is totally artificial, and then you can try to get it to work in a useful fashion." Fields hopes his new techniques may someday solve a few of the many puzzles biology still poses, as the yeast two-hybrid did before.