Robert Karl Stonjek
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 Posted: Mon Jul 21, 2008 5:41 am Post subject: News: Researchers Discover Remnant of an Ancient 'RNA World' |
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Researchers Discover Remnant of an Ancient 'RNA World'
(PhysOrg.com) -- Some bacterial cells can swim, morph into new forms and
even become dangerously virulent - all without initial involvement of DNA.
Yale University researchers describe Friday in the journal Science how
bacteria accomplish this amazing feat - and in doing so provide a glimpse of
what the earliest forms of life on Earth may have looked like.
To initiate many important functions, bacteria sometimes depend entirely
upon ancient forms of RNA, once viewed simply as the chemical intermediary
between DNA>s instruction manual and the creation of proteins, said Ronald
Breaker, the Henry Ford II Professor of Molecular, Cellular and
Developmental Biology at Yale and senior author of the study.
Proteins carry out almost all of life>s cellular functions today, but many
scientists like Breaker believe this was not always the case and have found
many examples in which RNA plays a surprisingly large role in regulating
cellular activity. The Science study illustrates that - in bacteria, at
least - proteins are not always necessary to spur a host of fundamental
cellular changes, a process Breaker believes was common on Earth some 4
billion years ago, well before DNA existed.
"How could RNA trigger changes in ancient cells without all the proteins
present in modern cells? Well, in this case, no proteins, no problem," said
Breaker, who is also a Howard Hughes Medical Institute investigator.
Breaker>s lab solved a decades-old mystery by describing how tiny circular
RNA molecules called cyclic di-GMP are able to turn genes on and off. This
process determines whether the bacterium swims or stays stationary, and
whether it remains solitary or joins with other bacteria to form organic
masses called biofilms. For example, in Vibrio cholerae, the bacterium that
causes cholera, cyclic di-GMP turns off production of a protein the
bacterium needs to attach to human intestines.
The tiny RNA molecule, comprised of only two nucleotides, activates a larger
RNA structure called a riboswitch. Breaker>s lab discovered riboswitches in
bacteria six years ago and has since shown that they can regulate a
surprising amount of biological activity. Riboswitches, located within
single strands of messenger RNA that transmit a copy of DNA>s genetic
instructions, can independently "decide'' which genes in the cell to
activate, an ability once thought to rest exclusively with proteins.
Breaker had chemically created riboswitches in his own lab and - given their
efficiency at regulating gene expressions - predicted such RNA structures
would be found in nature. Since 2002, almost 20 classes of riboswitches,
including the one described in today>s paper, have been discovered, mostly
hidden in non-gene-coding regions on DNA.
"We predicted that there would be an ancient 'RNA city' out there in the
jungle, and we went out and found it,'' Breaker said.
Bacterial use of RNA to trigger major changes without the involvement of
proteins resolves one of the questions about the origin of life: If proteins
are needed to carry out life>s functions and DNA is needed to make proteins,
how did DNA arise?
The answer is what Breaker and other researchers call the RNA World. They
believe that billions of years ago, single strands of nucleotides that
comprise RNA were the first forms of life and carried out some of the
complicated cellular functions now done by proteins. The riboswitches are
highly conserved in bacteria, illustrating their importance and ancient
ancestry, Breaker said.
Understanding how these RNA mechanisms work could lead to medical treatments
as well, Breaker noted. For instance, a molecule that mimics cyclic di-GMP
could be used to disable or disarm bacterial infections such as cholera, he
said.
Provided by Yale University
http://www.physorg.com/printnews.php?newsid=135522723
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Robert Karl Stonjek |
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