Re: [asa] Early evolutionary mechanism found

From: David Campbell <>
Date: Wed Jan 09 2008 - 13:57:28 EST

Here's the original abstract from Nature. Basically, the most popular
current model for the origin of life involves an RNA-based stage ("RNA
world") in which RNA functioned as both the carrier of genetic
information (as DNA does today) and as the primary catalyst to
implement this genetic information into chemical reactions in the cell
(a job mainly done by proteins today). This study carefully examined
a modern-day protein-RNA complex, looking for hints of how such a
structure might develop from an initial RNA only system.

Structure of a tyrosyl-tRNA synthetase splicing factor bound to a
group I intron RNA
Paul J. Paukstelis1, Jui-Hui Chen2, Elaine Chase2, Alan M.
Lambowitz1,3 & Barbara L. Golden2,3

Institute for Cellular and Molecular Biology, Department of Chemistry
and Biochemistry, and Section of Molecular Genetics and Microbiology,
School of Biological Sciences, University of Texas at Austin, Austin,
Texas 78712, USA
Department of Biochemistry, Purdue University, West Lafayette, Indiana
47907, USA
These authors contributed equally to this work.
Correspondence to: Alan M. Lambowitz1,3 Barbara L. Golden2,3
Correspondence and requests for materials should be addressed to
A.M.L. (Email: or B.L.G. (Email:

The 'RNA world' hypothesis holds that during evolution the structural
and enzymatic functions initially served by RNA were assumed by
proteins, leading to the latter's domination of biological catalysis.
This progression can still be seen in modern biology, where ribozymes,
such as the ribosome and RNase P, have evolved into protein-dependent
RNA catalysts ('RNPzymes'). Similarly, group I introns use
RNA-catalysed splicing reactions, but many function as RNPzymes bound
to proteins that stabilize their catalytically active RNA structure1,
2. One such protein, the Neurospora crassa mitochondrial tyrosyl-tRNA
synthetase (TyrRS; CYT-18), is bifunctional and both aminoacylates
mitochondrial tRNATyr and promotes the splicing of mitochondrial group
I introns3. Here we determine a 4.5- co-crystal structure of the
Twort orf142-I2 group I intron ribozyme bound to splicing-active,
carboxy-terminally truncated CYT-18. The structure shows that the
group I intron binds across the two subunits of the homodimeric
protein with a newly evolved RNA-binding surface distinct from that
which binds tRNATyr. This RNA binding surface provides an extended
scaffold for the phosphodiester backbone of the conserved catalytic
core of the intron RNA, allowing the protein to promote the splicing
of a wide variety of group I introns. The group I intron-binding
surface includes three small insertions and additional structural
adaptations relative to non-splicing bacterial TyrRSs, indicating a
multistep adaptation for splicing function. The co-crystal structure
provides insight into how CYT-18 promotes group I intron splicing, how
it evolved to have this function, and how proteins could have
incrementally replaced RNA structures during the transition from an
RNA world to an RNP world.

On Jan 9, 2008 11:06 AM, Jim Armstrong <> wrote:
> Scientists Find Missing Evolutionary Link
> <Scientists%20Find%20Missing%20Evolutionary%20Link>

Dr. David Campbell
425 Scientific Collections
University of Alabama
"I think of my happy condition, surrounded by acres of clams"
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Received on Wed Jan 9 13:58:33 2008

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