“What field of science you belong to depends on what questions you're asking,” says Nikolaus Rajewsky, who is formally trained as a physicist. “Having said this, I am a biologist.” Rajewsky, who joins the Max Delbrück Center (MDC) in Berlin next month, has frequently reformulated his questions. This is why his career has had such a broad span: mathematics, informatics and biology. (See CV)

His questions at his current base of New York University have focused on 'microRNAs' — short pieces of RNA that help regulate vital pathways such as insulin secretion and cholesterol synthesis, but whose mechanisms of action are still not understood. That is as hard-core as biology gets — but biology was the first subject Rajewsky dropped in school.

After a PhD in theoretical physics from the University of Cologne (where he also took a master's in piano-playing), Rajewsky took a summer course at Princeton University called 'biology for mathematicians' in 1999. “It was then that I decided on biology,” he says. He took up a postdoc position investigating regulatory elements in different genomes at Rockefeller University. “At that time, I knew little more about biology than the double helix and Darwin's theories,” he says.

Now a much-courted expert in bioinformatics, Rajewsky taught himself biology — from books, seminars and the “inspiring” scientific environment of Rockefeller.

“The questions I'm asking are biological ones,” he says, “and the tools I'm using are mostly informatics and wet-lab experiments.” He advises every biology student to get a solid education in bioinformatics: “You'll need it.”

His new appointment also covers Berlin's Charité medical school. “I like the possibility of bringing basic science to clinical institutions that the MDC opens up,” he says. “One of my long-term aims is to find out whether microRNAs might be competent for treating diseases.”

Leaving New York is not easy, he says. “There is this special American spirit: everyone has the right to be happy. And Americans complain a lot less than Germans do.”

Despite worries that Europe lags behind in genomics and systems biology, he is happy to be returning to Germany. “I want to bring home some of the things I learned in the United States,” he says. “I feel like a 'European American'.”

He and his wife, a pianist, are looking forward to the greater cultural variety of Europe. “Berlin in particular is a melting pot of science and culture,” he says. He still plays the piano most mornings. “I feel healthy when I'm playing, in every sense.”