> No, I think you are right. In my new education, I am learning
> that exons are regions of the DNA that are translated to RNA,
> and then bonded together. i.e. in a degraded version of the pretty
> picture on page 199 of my book, you have
>
> <--exon---><-intron-><------exon----><--intron--->
>
> and so forth, and only the exons are coded. That is, the introns
> can have the cool inhibitors and stuff that Gene was talking about,
> and Mr. DNA doesn't have to worry about coding for cyanide or
> something accidentally (since those parts don't code).
>
> After translation, you get <--exon---><------exon---->...
> with all the introns gone, GONE, GONE!!! The point being that
> any reverse translation process would have to take the string of
> exons, figure out where the introns had been, and what the introns
> had been made of in the first place, and so forth.
>
> Now another possibility strikes: if one could get this far, then
> with my untrained imagination, I can envision enzymes that would
> notice similarities of the exon string to the original DNA, grab
> the new polypeptide, tear apart the exons, and insert the introns back into
> (approximately) the right places. Of course there would be errors
> introduced if the ends of the new exons had been changed. Gene? Is
> this the raving of a molecular biology novitiate, or does a magical
> enzyme like this exist in theory or practice?
I am not aware that such an enzyme exists. This is not saying a lot,
though. It is a very interesting idea, but I see a few problems with it.
First, I imagine that such an enzyme would be tailored to match the codon
usage of the organism of which it is a part, yes? Otherwise, bad things
might happen. You'll need to solve the degeneracy problem.
Second, what if there are multiple copies of the gene (a not uncommon
event). The enzyme or, let's be a little more real, multienzyme complex,
would have to pick the right one? Would this matter in your scenario?
Let's call our multienzyme complex an antiribosome, since it is
reverse-translating the protein.
I think it would be more plausible if you didn't have your antiribosome
rip apart the extant DNA sequence...it would be better if it just copied
the relevant portions (the introns) onto its protein-RNA template and then
reverse transcribed the whole RNA sequence back into the genome, picking a
spot to ligate the newly made DNA sequence into.
Thirdly, and least importantly, what sort of practical value would this
anti-ribosome have...in terms of survival value, I mean. :-)
Gene
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Gene D. Godbold, Ph.D. Lab: 804 924-5167
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