Reverse Translation

[Sorcerer]

I think I just had a brilliant idea, and since I am feeling generous I am gonna share it with the world.

 

Since ribosomes can catalyse the formation of peptides using amino acids from information encoded in strands of RNA, why shouldn't they be able to catalyse the formation of RNA strands from nucleotides using the information encoded in proteins?

 

I think this may be on its way to a new hypothesis on abiogenesis..... Protein first hypothesis, I am sure there are some already out there, do they use a similar mechanism?

[VendingMenace]

If i may forward a tentative answer?

 

I believe that the reason why ribosomes cannot made RNA strands using protiens as a template is because the ribosome READS RNA but WRITES protiens.

 

Durring the process of translation the RNA is not altered at all. The Ribosome has no means by wich to process the RNA -- either to degrade it or to build it. Thus, the ribosome is not able to synthesize RNA.

 

Now, as to whether in theory you could find/biuld something that would make RNA using DNA as a template -- sure i guess. The information is there -- at least partly. The problem would lie in the fact that ammino acids are redundantly coded for. That is to say that there can be multiple sets of three nulceic acids that can code for a particulare ammino acid. Thus, for a particulare ammino acid, you would not know which set of nucleic acids to use. Wich set of three would be used would be depended on their concentration in surrounding environment. However, the sequence of amino acids DOES matter for the process of transcription (and translation too). Differeing sequences (that code for the same set of amino acids) can have different effects on regulation and expression. This is because these different sequences can intereact diferently with expressors, repressors, ect. Plus they could be more or less likely to form hairpin loops wich are used to regulate their expression (both transcription and translation).

 

SO there, at least, is one problem with the sequence of protein --> RNA. Given multiple acceptable (coding for the same sequences of amino acids) sequences of RNA, you would not be able to specify with one you wanted.

 

Another problem might be that it would be difficult to bring out the introns (the portion of DNA that is not transcripted, but may still have regulatory functions) as well as the promotor region and the stop codon. For these sections are not translated, merely trascripted. So it would be impossible (or at least unlikely, i suppose) to aquire them from protien --> RNA.

 

So there are two objections that i can come up with, at least right now.

 

This is not to say that the protien first hypothesis my not, ultimately, be right. I am just trying to point out what i see as flaws with it. Indeed the fact that protiens and RNA and DNA are intimately connected makes it very difficult to assign one priority. Though i think that the fact that the mechnism for translation is nucleic acid baised, is a strong argument for the priority of nucleic acids. And further, the fact that the ribozyme is RNA based would lead on to suspect that perhaps RNA was the first thing out there. And i do belive that this is what is belived by most biologist to be the case (though i could be wrong on that score).

 

Anyways, GREAT question. It made me think, and i love that. I would say, keep looking into it and wondering about it. Even in it doesn't pan out, the amount you learn by trying to find out, will be well worth the effort!

 

SWEET!

[Sorcerer]

Hmm yes your right, Ribosomes couldnt reverse traslate a protein.... it would need an almost entirely different system, something with doubles as tRNA (actually tRNA would serve this purpose) but carries 3 neucleotides (codon), something that doubles as rRNA, ie catalyses the polyermisation of nucleotides, and something that doubles as mRNA but this is the protein. I also don't see why the protein couldn't double as the rRNA as well as the mRNA. However I do see a problem with the protein folding, it would need to be a short peptide which allowed access to all of its amino acids, ie very little secondary and tertiary folding... without the folding then catalytic function would be non-existant, so that puts an end to my protein being a rRNA and mRNA doppleganger.

 

I don't really see a problem with the redundancy, you suggest that it plays a role in regulation, however I am hypothesising a mechanism for abiogenesis, the complexity needed for regulation wouldn't have yet arisen, just producing a codon would be sufficient.

 

My hypothesis now seems to be protein+tRNA first. A protein that catalyses the formation of tRNA and mRNA and also acts as a template for the formation of mRNA which codes for itself.

[Guest davidohagan]

I have the solution if you want to help work on the chemistry? The project may get swollowed up by big pharma... but I'm glad you two had the guts to think outside the box... David O'Hagan, San Diego....

[donkey]

I have the solution

I'm a bit confused, what do you have the solution to? producing RNA from a peptide sequence?

 

p.s. hi all

[Bluenoise]

DNA/RNA is pretty simple making it easy to read, it's all nice and laid out straight and alinged properly. Protein structure is really complex though. Alinging it in such a way that it could be read and translated by another protein may not be possible.

[Sorcerer]

Hi David, I would love to work on something like this, Im having such a hard time finding a job in science here in NZ......

 

Anyway, to further the idea, the protein sequence would bind to tRNA which is carrying a mRNA codon, this would then be bound to a neighbouring mRNA codon held to the coresponding tRNA and the amino acid on the protein. To do this a ribosome or something similar could hold the mRNA codon in place, while RNA polymerase joined the 3' and 5' ends. The resulting mRNA sequence would then be reverse transcribed by reverse transcriptase to produce DNA sequences lacking introns and not all identical since there are several codons for one amino acid.

[Sorcerer]

Could RNA polymerase catalyse the creation of its own mRNA? Providing there was tRNA, nucleotides and energy available?