The last few years have been very good to ribonucleic acid (RNA).
Decades after DNA took biology by storm, RNA was considered little more
than a link in a chain--no doubt a necessary link, but one that, by
itself, had little to offer. But with the discoveries of RNA
interference and microRNAs, this meager molecule has been catapulted to
stardom as a major player in genomic activity.
Now, a team of
scientists led by David Bartel, a professor in MIT's Department of
Biology, has discovered an entirely new class of RNA molecules.
in the journal Cell, the team describes identifying more than 5,000 of
these new molecules, termed 21U-RNAs, in the C. elegans worm. These new
RNAs are named after their distinctive features: Each molecule contains
21 chemical building blocks (or nucleotides), and each begins with the
chemical uridine, represented by the letter U (the only RNA nucleotide
not also found on DNA). In addition, each of the 5,000 different
21U-RNA molecules comes from one of two chromosomal regions.
"we can predict where additional 21U-RNA genes might reside," says
Bartel, who is also a member of the Whitehead Institute for Biomedical
Research and a Howard Hughes Medical Institute investigator. "Combining
these predictions with the 5,000 (21U-RNAs) that we experimentally
identified, we suspect that there are more than 12,000 different
21U-RNA genes in the genome." Because each gene typically produces a
unique 21U-RNA, a very large diversity of molecules is made.
are so many 21U-RNA genes spread out over such a wide swath of the
genome, but they all share common requirements for expression and
common structural features," says Bartel lab Ph.D. student J. Graham
Ruby, lead author on the paper.
Although the researchers haven't
yet identified a particular function for these molecules, they believe
that this uniform structure strongly indicates an important role.
Institute Professor and Nobel Laureate Phillip Sharp, a biologist who
was not part of the research team, supports this hypothesis. The fact
that 21U-RNAs share this "common structure and origin suggests an
important function," he says. "It requires function to conserve
Other members of the research team are affiliated
with the Broad Institute of MIT and Harvard and Pennsylvania State
University. This research was supported by the Prix Louis D from the
Institut de France and a grant from the National Institutes of Health.