They had figured out in 1975 how to make chemically reactive cellulose that would covalently bind to DNA and RNA (3). Stark’s group then made chemically reactive cellulose paper onto which they could attach RNA molecules from a gel. They then probed the entire paper with the complementary nucleic acid chain (4). “It actually worked the first time we tried it,” says Stark.
Stark’s sense of humor came through when they named the technique “Northern blotting” as a joke on Southern blotting, which Edwin Southern at Oxford University had developed for DNA detection (5). Similarly, Stark’s group did the first demonstration of the idea of transferring proteins out of gels for detection (6, 7).
It was also at Stanford that Stark’s group discovered PALA, an abbreviation for N-phosphonacetyl-L-aspartate (8). The molecule is the analog of aspartate transcarbamylase’s transition state. Stark’s group discovered that PALA was a strong inhibitor of aspartate transcarbamylase and that it could enter mammalian cells to block pyrimidine nucleotide biosynthesis.
With PALA, Stark and colleagues went on to discover the giant polypeptide CAD that contained aspartate transcarbamylase, carbamyl phosphate synthetase and dihydro-orotase, all involved in pyrimidine synthesis. By studying CAD, Stark’s group was one of the first to show gene amplification in mammalian cells.
An American in London
In 1983, after 20 years at Stanford, Stark landed in London at the Imperial Cancer Research
Fund. His research interests had moved from protein biochemistry to cellular and molecular biology, and he was interested in interferon-dependent signaling, an area in which he worked in collaboration with Ian Kerr at the U.K. Medical Research Council.
“London is a wonderful place to live,” says Stark. “We were very privileged, because we owned a house in California that we were basically able to trade for a nice house in central London.” Stark says that the environment at ICRF was also special. “My lab was completely funded. I didn’t have to write any grants. All I had to do was show up for a review every five years,” he explains. “It was heaven for somebody like me who wanted to primarily do research.”
Part of his group in London worked on mechanisms of gene amplification, and the rest worked on interferon signaling pathways, research that later led to the discovery of the JAK-STAT pathway (9). The group also developed an approach called validation-based insertional mutagenesis (10).
But Stark’s idyllic world was in for a nasty surprise nine years later. “I realized I was going to have to retire in the British system in a couple of more years!” he says. Stark would have had to have stopped working in 1995 at age 62.