[meteorite-list] New Study Brings Scientists Closer to the Origin of RNA

[Ron Baalke]

http://www.news.gatech.edu/2013/12/23/new-study-brings-scientists-closer-origin-rna

New Study Brings Scientists Closer to the Origin of RNA
Georgia Institute of Technology
December 23, 2013 

One of the biggest questions in science is how life arose from the chemical 
soup that existed on early Earth. One theory is that RNA, a close relative 
of DNA, was the first genetic molecule to arise around 4 billion years 
ago, but in a primitive form that later evolved into the RNA and DNA molecules 
that we have in life today. New research shows one way this chain of events 
might have started.

Today, genetic information is stored in DNA. RNA is created from DNA to 
put that information into action. RNA can direct the creation of proteins 
and perform other essential functions of life that DNA can't do. RNA's 
versatility is one reason that scientists think this polymer came first, 
with DNA evolving later as a better way to store genetic information for 
the long haul. But like DNA, RNA also could be a product of evolution, 
scientists theorize.

Chemists at the Georgia Institute of Technology have shown how molecules 
that may have been present on early Earth can self-assemble into structures 
that could represent a starting point of RNA. The spontaneous formation 
of RNA building blocks is seen as a crucial step in the origin of life, 
but one that scientists have struggled with for decades.

"In our study, we demonstrate a reaction that we see as important for 
the formation of the earliest RNA-like molecules," said Nicholas Hud, 
professor of Chemistry and Biochemistry at Georgia Tech, where he's also 
the director of the Center for Chemical Evolution.

The study was published Dec. 14 online in the Journal of the American 
Chemical Society. The research was funded by the National Science Foundation 
and NASA.

RNA is perfect for the roles it plays in life today, Hud said, but chemically 
it's extraordinarily difficult to make. This suggests that RNA evolved 
from simpler chemical couplings. As life became more chemically complex 
and enzymes were born, evolutionary pressures would have driven pre-RNA 
into the more refined modern RNA.

RNA is made of three chemical components: the sugar ribose, the bases 
and phosphate. A ribose-base-phosphate unit links together with other 
ribose-base-phosphate units to form an RNA polymer. Figuring out how the 
bond between the bases and ribose first formed has been a difficult problem 
to address in the origins of life field, Hud said.

In the study, Hud's team investigated bases that are chemically related 
to the bases of modern RNA, but that might be able to spontaneously bond 
with ribose and assemble with other bases through the same interactions 
that enable DNA and RNA to store information. They homed in on a molecule 
called triaminopyrimidine (TAP).

The researchers mixed TAP with ribose under conditions meant to mimic 
a drying pond on early Earth. TAP and ribose reacted together in high 
yield, with up to 80 percent of TAP being converted into nucleosides, 
which is the name for the ribose-base unit of RNA. Previous attempts to 
form a ribose-base bond with the current RNA bases in similar reactions 
had either failed or produced nucleosides in very low yields.

"This study is important in showing a feasible step for how we get the 
start of an RNA-like molecule, but also how the building blocks of the 
first RNA-like polymers could have found each other and self-assembled 
in what would have been a very complex mixture of chemicals," Hud said.

The researchers demonstrated this property of the TAP nucleosides by adding 
another molecule to their reaction mixture, called cyanuric acid, which 
is known to interact with TAP. Even in the unpurified reaction mixture, 
noncovalent polymers formed with thousands of paired nucleosides.

"It is amazing that these nucleosides and bases actually assemble on their 
own, as life today requires complex enzymes to bring together RNA building 
blocks and to spatially order them prior to polymerization,"said Brian 
Cafferty, a graduate student at Georgia Tech and co-author of the study

The study demonstrated one possible way that the building blocks for an 
ancestor of RNA could have come together on early Earth. TAP is an intriguing 
candidate for one of the first bases that eventually led to modern RNA 
molecules, but there are certainly others, Hud said. 

Future work, in Hud's lab and by other laboratories in the Center for 
Chemical Evolution, will investigate the origins of RNA's phosphate backbone, 
as well as other pathways toward modern RNA.

"We're looking for a simple, robust chemistry that can explain the earliest 
origin of RNA or its ancestor," Hud said.

This research is supported by the National Science Foundation (NSF) Center 
for Chemical Evolution under award number CHE-1004570, and the NASA Exobiology 
Program under award number NNX13AIO2G. Any conclusions or opinions are 
those of the authors and do not necessarily represent the official views 
of the sponsoring agencies.

Research News
Georgia Institute of Technology
177 North Avenue
Atlanta, Georgia 30332-0181 USA

Media Relations Contacts: Brett Israel (404-385-1933) (brett.israel at comm.gatech.edu) 
or John Toon (404-894-6986) (jtoon at gatech.edu)

Writer: Brett Israel

Contact Information

Brett Israel

404-385-1933

brett.israel at comm.gatech.edu

Contact E-mail: brett.israel at comm.gatech.edu