DNA downloads alone
The information in DNA can be copied into new molecules without proteins' help.
"Nature Science Updates", 5 February 2002
PHILIP BALL

Chemists have reproduced the basic process of information transfer 
central to all life without the catalysts that facilitate it in living cells.
(1) 

They show that DNA alone can pass its message on to subsequent 
generations. Many researchers believe that DNA-like molecules acted 
thus to get life started about four billion years ago - before catalytic 
proteins existed to help DNA to replicate.

The experiment, carried out by David Lynn and co-workers at Emory 
University in Atlanta, Georgia, might create a new basis for the precise 
synthesis of useful polymer materials. It may even hasten the advent of 
synthetic biology: the creation of life from scratch.

History repeats itself

Synthetic self-replicating molecules have been made in the lab at least 
three times before. But in all these cases the replicating molecules were 
given a substantial helping hand. 

Before, each molecule acted as a template on which its copy was 
constructed from two ready-made halves. In other words most of the 
information in the copy was present already in the fragments from which 
it was made. It was rather like reproducing the information in this 
sentence simply by pasting it together from two already-written halves.

In contrast, Lynn and colleagues paste each letter in place, one by one. 
They make, not a copy, but a complementary molecule, containing the 
same information but in a different code. It is rather like making a copy of 
one of these sentences but translated into French.

In the cell, DNA itself contains two such complementary molecules, each 
one a chain of molecular units, stuck together in the double helix. When 
DNA replicates before a cell divides, these complementary strands part 
and each acts as a template to guide the synthesis of a fresh strand.

Each DNA strand contains all the information needed to make a new 
strand. There are four different kinds of molecular unit, and the sequence 
of these along the strand determines the sequence of units assembled in 
the new strand. Enzymes drive this assembly process.

Stranded

Lynn's group has found a way to do without the enzymes, so that a 
single strand of DNA can act as a template for the assembly of its 
complementary strand. Scientists have achieved this before, but 
imperfectly: only one of the four types of DNA unit acted as a template, 
and the complementary strand wasn't always the same length as the 
template.

The Emory group uses a new trick to join the components together on a 
DNA template. The chemical links between successive units in the new 
strand aren't like those in DNA itself. Instead they are amide linkages, 
like those that unite proteins' molecular units, which are also chain-like 
molecules laden with information. This makes the assembly of the new 
strand more accurate.

Amide-linked DNA chains can help units of true DNA to join together. 
So the researchers hope to achieve the reverse process of templating 
DNA using amide-linked DNA. This might then enable the two kinds of 
molecule to support their mutual replication, allowing the possibility of 
molecular evolution and the appearance of life-like complexity. 

References
Li, X., Zhan, Z.-Y. J., Knipe, R. & Lynn, D. G. DNA-catalyzed polymerization.
Journal of the American Chemical Society, 124, 746-747, (2002).

Oryginal:
http://www.nature.com/nsu/020204/020204-2.html
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DNA-Catalyzed Polymerization 
Xiaoyu Li, Zheng-Yun J. Zhan, Rachel Knipe, and David G. Lynn.
Journal of the American Chemical Society, 124 (5), 746 -747, 2002. 

Abstract: Native DNA oligomers are shown to be stereoselective 
catalysts for the polymerization of 5'-amino-3'-acetaldehyde-modified 
thymidine/adenosine nucleosides through reductive amination. The 
reaction follows step-growth kinetics to read the encoded sequence and 
chain-length information in the antiparallel direction. Single mismatches 
in the template are selected against at a level of >100:1. A method is 
therefore established to translate biopolymer-encoded information 
stereoselectively into sequence- and chain-length specific synthetic 
polymers.

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This research does appear to change the rules for abiogenesis, so ably 
summarised below by John Maynard Smith:
"The problem of the origin of life, then, is to explain how entities with 
these properties could originate from non-living matter, without of 
course invoking natural selection as a cause. If we imagine the simplest 
conceivable organism whose hereditary mechanism depends on the 
processes of nucleic acid replication and protein synthesis as we know 
them from existing organisms, it would have to possess enough DNA to 
specify all the varieties of tRNA, the protein and RNA components of 
the ribosomes, the activating enzymes associated with the 20 amino 
acids, the various enzymes which replicate the DNA and make an RNA 
transcript of it, and more besides. ... It is impossible that an organism of 
this degree of complexity should arise by physico-chemical processes, 
without natural selection." 
Maynard Smith J., "The Theory of Evolution," [1958], Cambridge 
University Press/Canto: Cambridge UK, Third Edition, 1993, reprint, 
pp.110-111.

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