This Echo is READ ONLY !   NO Un-Authorized Messages Please!
 ~~~~~~~~~~~~~~~~~~~~~~~~   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

BioMed Central Limited
London, U.K.

Contact:
Gemma Bradley, press{at}biomedcentral.com, +44 (0) 20 7323 0323

Embargo until 28 May 2003, 13:00 GMT

Born under the sun: UV light and the origin of life

Early evolution of life as we know it may have depended on DNA's
ability to absorb UV light. This insight into the early moments of
life on Earth comes from research published today in the journal BMC
Evolutionary Biology. 

The research fills in one of the major gaps in our understanding
about the origins of life: how single molecules were able to join
together to create the self-replicating long chain molecules of RNA,
the precursors of DNA. It "sheds new light on the earliest steps of
evolution," write Armen Mulkidjanian and his colleagues from
Osnabruck University, Germany and National Institutes of Health, USA.

With no ozone layer the primordial Earth was a hostile place. This
was especially true for long-chain molecules that would be broken up
by UV radiation, which was at 100 times today's level. Most existing
theories about how life evolved involve hiding the first life forms
away from the light. Instead, Mulkidjanian and his colleagues have
investigated the idea that high levels of UV light hitting the
primordial earth were vital to RNA's survival. 

The researchers used computer-modelling technology to assess the
ability of RNA to form from its constituent parts, sugar phosphates
and nitrogenous bases, with and without high levels of UV light. They
found that the ability of nitrogenous bases to absorb and disperse UV
radiation could protect the backbone of primordial RNA from breaks.
Under high levels of UV, RNA molecules were more stable than other
large molecules and the small molecules that join together to create
the RNA. This gave RNA molecules a selective advantage, so that their
levels then increased through the simulated process of natural
selection.  Moreover, part of the energy from the absorbed UV light
could have driven the elongation of RNA chains.

"The suggested mechanism turns the high UV levels on primordial Earth
from a perceived obstacle to the origin of life into the selective
factor that, in fact, might have driven the whole process", write the
authors. 

"It seems quite unlikely that the extremely effective UV-quenching by
all major nitrogenous bases is just incidental. We can assume that
these bases were selected to perform the UV-protecting function
before they became involved in the maintenance and transfer of
genetic information. In this (primordial) world the nitrogenous bases
served just as protecting units. Accordingly these units were
replaceable and variable. Exactly this variability could have paved
the way to the variability of the future genomes". 

Three of the four nitrogenous bases that protected RNA from UV on
primordial Earth are the same as those that make up the genetic code
of DNA. Ironically, the ability of DNA to absorb UV light is now
responsible for many skin cancer deaths. When the bases of DNA absorb
UV light they often suffer structural damage, although the DNA
backbone remains intact. If this damage occurs within a gene it can
lead to the alteration of that gene, which may cause cancer. 

Notes for editor

Upon publication on Wednesday 28th May at 13:00 GMT, this article
will be freely available online via
http://www.biomedcentral.com/1471-2148/3/12/abstract , according to
BioMed Central's policy of open access to research articles: 

    Survival of the fittest before the beginning of life.
    Selection of the first oligonucleotide-like polymers by UV light
    Armen Y. Mulkidjanian, Dmitry A. Cherepanov, Michael Y. Galperin
    BMC Evolutionary Biology

Please publish the URL in any news report so that your readers will
be able to read the original paper.

Contact the authors:

Dr. Mulkidjanian can be contacted by phone on +49-541-969-2871 or by
email at mulkidjanian{at}biologie.uni-osnabrueck.de

Dr. Galperin can be contacted by phone on +1-301-435-5910 or by email
at galperin{at}ncbi.nlm.nih.gov

For any further information please contact Gemma Bradley by email at 
press{at}biomedcentral.com or by phone on +44 (0)20 7323 0323 x2331.

BMC Evolutionary Biology (http://www.biomedcentral.com/bmcevolbiol/)
is published by BioMed Central (http://www.biomedcentral.com), an
independent online publishing house committed to providing immediate
free access to peer-reviewed biological and medical research. This
commitment is based on the view that open access to research is
essential to the rapid and efficient communication of science. In
addition to open-access original research, BioMed Central also
publishes reviews and other subscription-based content.

 - END OF FILE -
==========

@Message posted automagically by IMTHINGS POST 1.30
---