Here's a quote from Strickberger on 2 ways
protein synthesis might have evolved. I agree
with both.  And think both happened at the same
time.

"Protein synthesis might then have evolved through
(2 ways) specific amino acids directly interacting
with specific nucleotide sequences...."

One idea is that first coding would favor two divisions
hydrophilic or hydrophobic and later this would be
refined to what we have today. But I say why have two
at first? That seems unrealistic and highly complicated
and refined for  the origin. 

Instead I suggest
that the first peptides to be selected were all
or mostly hydrophilic. Thus those that could react
in water were exclusively selected at first. 
Hydrophobic would
be a later reaction against water.

Almost all nucleotides (and they are sparse in prebiotic
experiments)   are purines. 
Also pyrimidines
may have been selected against because of UV caused
dimers.
Also we have 3 bases in a codon to separate bases
and prevent dimers.
For these and other reasons most of the earliest 
RNA strands would be purines, and would NOT 
be two pyrimidines together ( could make dimer).

Thus we have two separate conditions going on
at the same time:
1. chemical selection favoring hydrophilic amino acids.
2. chemical selection favoring purine nucleotides.

Together they set up the first match
mostly hydrophilic amino acids with mostly
purine coding. (Any mismatch would be 
chemically selected against)

Later (in a way that is still very murky)
its opposite would be chemically selected for
due to the improvements they would bring:
hydrophobic amino acids , and pyrimidine
nucleotides

******

"...or, perhaps through indirect placement of 
amino acids into such sequences by intermediary
adaptor molecules that brought amino acids to the
nucleotide chain."

I think the 'intermediary adaptor molecules were
polyphosphate chains (pre-ATP). Any nucleotides
or peptides that were in the vicinity of polyphosphate 
chains would have the advantage they gave
(chemical energy) and would be chemically selected.

Those isolated without polyphosphate chains 
would have no chemical energy source.

Thus we would have islands of prebiotic chemistry
where there was polyphosphate chains. The rest
of the prebiotic soup would be mostly inert to change.

Comment?
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 * RgateImp.MoonDog.BBS at 6/15/04 5:03:05 PM