A pair of U.S. scientists involved in the study of gene activity were awarded the Nobel Prize in physiology or medicine on Monday for their discovery of microRNA and its role in post-transcriptional gene regulation.

Victor Ambros, a professor at the University of Massachusetts Medical School, and Gary Ruvkun, a professor of genetics at Massachusetts General Hospital and Harvard Medical School, discovered microRNA, a new class of tiny RNA molecules that play a crucial role in gene regulation.

“Their groundbreaking discovery revealed a completely new principle of gene regulation that turned out to be essential for multicellular organisms, including humans,” the Nobel Foundation said in announcing the award.