For people who know about RNA mostly from its place in the central dogma of biology—DNA➙RNA➙Protein—this story may hold a number of surprises.
That handy equation, taught in Biology 101 courses around the globe, sums up the flow of genetic information in living organisms: how our DNA gets copied into RNA, which then gets converted into proteins, the building blocks of our cells, our bodies.
Originally, the RNA referred to in this equation—messenger RNA, or mRNA, the type that codes for proteins—was the only kind known to science. However, over the years, it has become clear that there are many, many other kinds.
“The world of RNA has proven to be a big and fascinating place,” says Marv Wickens, a CALS professor of biochemistry and leading pioneer in RNA research. “I’ve come to think of it as a Fellini movie, full of strange and unexpected characters.”
These Felliniesque characters are all the non-coding RNAs that exist in nature—the kinds that don’t code for proteins. They go by names like small interfering RNA, piwi-interacting RNA, microRNA, long non-coding RNA, small nuclear RNA—the list goes on and on. Together they far outnumber messenger RNAs in the cell; while only 3 percent of the human genome gets made into proteins (via messenger RNA), a full 80 percent gets copied into RNA.
What are all of these other RNAs doing? Lots of important and surprising things, scientists are discovering.
Over the past few decades, RNA, a close chemical cousin of DNA, has proven itself to be a much more versatile molecule than originally thought—far more than just a passive messenger.
The first big surprise came in the 1980s when it was shown that RNA can have catalytic activity, meaning that it can perform chemical reactions inside the cell. Originally assumed to be inert, like DNA, scientists found RNA molecules that could edit their own sequence—expunging a segment of their own genetic code.
Later, RNAs were discovered at the heart of important cellular machines, or enzymes, performing critical catalytic reactions, including those at the heart of the cell’s information transfer system. Previously only proteins were thought capable of such enzymatic feats.