Three researchers who studied how cells shuttle around essential molecules in tiny intracellular sacs have won this year’s Nobel Prize in physiology or medicine. James Rothman of Yale University; Randy Schekman of the University of California, Berkeley; and Thomas Südhof of Stanford University earned the award "for their discoveries of machinery regulating vesicle traffic, a major transport system in our cells," according to the announcement from the Nobel Assembly at Karolinska Institute in Stockholm.

The three researchers independently unraveled basic cellular mechanisms several decades ago—in Schekman's case, almost 40 years ago. Although mistakes in cellular transport systems can cause a variety of diseases—including diabetes and neurological and immunological disorders—their work has not yet led to any new drugs or therapies, but it has helped others develop diagnostic tests.

Schekman, who's also an investigator at the Howard Hughes Medical Institute (HHMI), a former editor of the Proceedings of the National Academy of Sciences, and the current editor-in-chief of the open access journal eLife , studied intracellular transport in yeast cells in the 1970s. He identified cells whose transport machinery didn't function properly, causing the vesicles to pile up in the cell, and identified the mutated genes responsible for those problems—a discovery that helped understand how intracellular traffic works under normal circumstances.

Rothman, who has been at Yale since 2008, is honored for work he did on vesicular transport in mammalian cells while at Stanford University, Princeton University, and the Memorial Sloan-Kettering Cancer Center in the 1980s and 1990s. Rothman showed how a protein complex enables vesicles to dock and fuse with their target membranes, a process in which proteins on the sacs and their targets bind to each other like the two sides of a zipper. (Each half of the zipper complex has to match the other precisely, allowing the cell to direct compounds exactly where they need to do.) The mechanism is used both inside a cell and when a vesicle arrives at a cell from the outside to deliver its contents.

Südhof was born in Germany and came to the University of Texas Southwestern Medical Center in Dallas in 1982 to work in the lab of Michael Brown and Joseph Goldstein, who both won a Nobel in 1985. Südhof receives his share of this year's prize for transport studies as well—in his case, of how neurotransmitters, an all-important class of chemical messengers, are transported between neighboring nerve cells.

In the 1990s, Südhof— now also an HHMI investigator , like Schekman—identified proteins that respond to an influx of calcium into the neuron, allowing other, nearby proteins to bind to vesicles containing neurotransmitters and let their content flow into the nerve cell. His work helped explain how nervous systems can achieve their amazing speed and temporal precision.

At today's press conference, Göran K. Hansson, secretary of the Nobel Committee, said he had had reached Schekman and Rothman this morning. "Both were delighted, surprised, and happy," he said. "They were delighted to share [the award] with others in this combination."

“My first reaction was, 'Oh, my god!' ” Schekman said in a press release issued by Berkeley this morning . “That was also my second reaction.”