On Thu, Jul 26, 2001 at 02:22:45AM -0700, Robert J. Bradbury wrote:
>
> > possibly make some of the potentially dangerous genes
> > brittle in the sense that any mutation there will disable
> > the cell (how to to achieve that?).
>
> I love it on those rare instances when I'm actually ahead
> of Anders on the curve... :-)
:-)
> First you make the genetic code brittle in terms of no
> "redundancy". To do this optimally, you have to study
> the mechanisms driving transition & transversion frequencies
> (http://www.iona.edu/faculty/csackerson/genetics/mutation.htm)
> and "rig" the code such that the most likely mutations
> generate either STOP codons or "radical" amino-acid changes
> (i.e. + charge to - charge, hydrophobic to hydrophilic, etc.).
> I haven't tried to do this yet -- I suspect to really
> get it right requires a fair amount of simulation based
> on existing genomes.
Nice! But it only works if you re-design the genetic code. Otherwise it
seems to require that you design your proteins to contain these "brittle"
amino acids are in the right places and functional for it. That sounds
awfully like a constrained inverse protein folding problem.
> You can drive the mutation rate to very low levels if
> you work on it enough. Nature doesn't generally seek
> really low mutation rates, so this is an unexplored
> part of the phase space.
Maybe we should start looking for interesting bacteria close to Chernobyl,
in uranium mines or simply set up evolution in high radiation environments
to see if we can get some fun solutions.
> > Linda Nagata did a nice trick in her _Limit of Vision_ to show
> > how you could get around such a metabolic constraint on a GMO
> > both short term and long term
>
> I'll have to read that -- I'm suspicious that she may have leaped
> the fence of statistical improbability. If there your error rate is
> 10^-50, *it* can happen, but I'm not going to lose any sleep over it.
<spoiler>
Her genetic engineers had used octopine and nopaline as essential
substances for survival and reproduction, respectively. But one of the main
characters discovered that crown galls contained enough of these substances
to keep the biotech beasties alive and healthy. Later, the biotech manages
to form some kind of symbiosis with the agrobacterium cells producing the
substances, becoming independent of the original source.
Of course, the involved engineers had never planned on having their
creations out in the wild anyway, so they were likely not that careful in
selecting anything truly rare to control them. I guess they were in the
same biotech safety class as the engineers working for Jurassic Park :-)
</spoiler>
-- ----------------------------------------------------------------------- Anders Sandberg Towards Ascension! asa@nada.kth.se http://www.nada.kth.se/~asa/ GCS/M/S/O d++ -p+ c++++ !l u+ e++ m++ s+/+ n--- h+/* f+ g+ w++ t+ r+ !y
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