Scientists discover new class of
RNAs
CAMBRIDGE, Mass. (January 10, 2007) — The last
few years have been very good to RNA. Decades after
Watson and Crick’s central dogma 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.
As sequencing technology continues to ramp up, RNA
influence appears more widespread by the month. Recently,
a team of scientists in the lab of Whitehead Member
and Howard Hughes Medical Institute Investigator David
Bartel discovered an entirely new class of RNA molecules.
Reporting 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 5000 different 21U-RNA
molecules come from one of two chromosomal regions.
And while the 21Us themselves have diverse sequence
patterns, the DNA sequences residing just outside those
that give rise to each 21U are identical.
“Using the sequence pattern, we can predict where
additional 21U-RNA genes might reside,” says Bartel.
“Combining these predictions with the 5,000 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.
“There are so many 21U-RNA genes spread out over
such a wide swathe of the genome, but they all share
common requirements for expression and common structural
features,” says Bartel-lab PhD student J. Graham
Ruby, lead author on the paper.
Because of this, the researchers believe that even though
they haven’t yet identified a particular function
for these molecules, this uniform structure strongly
indicates an important role.
MIT professor and Nobel Laureate Phillip Sharp, 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 specificity.”
This research was supported by the Prix Louis D from
the Institut de France and a grant from the National
Institutes of Health.
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