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Why does post-transcriptional processing of eukaryotic mRNA involve addition of a 3' polyA tail, rather than one of polyU, -G, or -C?

David
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Raju Biology
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  • Quite interesting question. It also evokes the question of abundance / availability, since ATP (which is also used for poly-adenylation - besides its role in providing energy for many biochemical reactions), also appears to be the most produced and consumed molecule in humans, link – tsttst Jul 16 '16 at 23:50
  • This is likely an evolutionary selection result, with A having won out. Most likely dude to availability and stability. Once addition of As to ends of RNA increased fitness of RNA, it was selected for. Simalar question is why is ATP often a substrate when GTP and CTP and such carry near equiv energy. – SciEnt Jul 17 '16 at 15:28
  • @SciEnt Please answer questions as answers, not as comments. That's what it says when you click in the comment box. – David Jul 17 '16 at 21:46
  • @David everytime i amswer like you have without any citation i get downvoted or told to cite. Thus my comment feels more appropriate – SciEnt Jul 18 '16 at 00:07
  • @SciEnt — I'm sorry but the text in the comment box means what it says. It is basic to the model that the Stack Exchange network follows. If you answer you have to be prepared for criticism. I accept your implied criticism of my answer as valid, and I have now added a reference. – David Jul 18 '16 at 07:09

2 Answers2

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As others have mentioned poly-A seems to be favoured because of higher concentrations of ATP with respect to other NTPs, due to its ubiquitous role. There is no real proof for this like most "why" questions. However, the ubiquitous presence of ATP is itself an evidence for a random selection of ATP and a subsequent expansion of its role. There is no thermodynamic explanation for this. The selection is likely to have been random.

Polyuridylation is also known to happen in eukaryotic cells (reviewed by Munoz-Tello et al., 2015) and one of the well known cases is that of the let-7 pre-miRNA (Heo et al., 2008). Polyuridylation marks this pre-miRNA for degradation.

WYSIWYG
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  • And then it's also interesting to ask why GTP has a similar but far less ubiquitous role than ATP and CTP and TTP (to my knowledge) have no such role at all. I like to think about these obviously contingent features evolution brought up ... and expand this idea to the notion of us humans assigning functions to observations that might simply be contingent. – AlexDeLarge Jul 18 '16 at 17:18
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Most probably because the concentration of ATP in cells is much higher than that of the other nucleoside triphosphates and there was no functional requirement for a particular base in the tail. Its main function seems to be to work with an appropriate nuclease system to regulate the mRNA lifetime (see, e.g. Wikipedia article).

David
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