Third Genetic Code Anyone?

نویسنده

  • Geoffrey North
چکیده

genome is a curious one, when so far as we know the specificity of those modifications depends on genome-encoded proteins. The hope of believers is that, once the modifications have been made they are 'self-replicating' — they guide similar modification of daughter chromatin. This remains a possibility, but so far at least there is little hard evidence for such self-replication, independent of sequence-specific DNA-binding proteins or RNAs. Whether or not they are self-perpetuating, histone modifications no doubt play some important role in gene regulation. The regulation of proteins by chemical modification is very widespread of course, and in many cases the modification works by attracting a second protein to the modified one; as, for example, in the case of ubiquitination, which leads to destruction of a protein by the proteasome. In a sense the modification is informational, acting as a tag that says 'do this', rather than working directly by its chemical effects on the modified protein. But I am not sure that this is a code in as clear a sense as the genetic one, where one type of information (a nucleic acid sequence) is converted into another (a protein sequence) — and, importantly, where nucleotide triplets can be strung together to encode a protein of arbitrary length and sequence. The capacity to make arbitrary messages is surely an important feature of a real code. There are other claimants: RNA sequences that determine sites of pre-mRNA splicing; DNA sequences supposed to influence the phasing of nucleosomes along chromatin; the chemical properties of amino acids that influence protein folding; and so on. As each eager new candidate comes along, it is invariably dubbed a new second genetic code — never a third or fourth genetic code.... Why is this? In the contemporary parlance of the internet age, a kind of crowd-sourced opinion is being made, a thumbs down to the claim, which, if truly meaningful and useful, would surely be taken up into general usage, to become the second genetic code. I would suggest we accord the one, universal genetic code its deserved special place by not nominating others to join it in a list. This year is the fiftieth anniversary of the great paper [1] describing the general form of the genetic code, a beautiful theoretical and genetic study making a strong case that proteins are encoded in polynucleotides by strings of contiguous, non-overlapping base triplets. This was soon …

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عنوان ژورنال:
  • Current Biology

دوره 21  شماره 

صفحات  -

تاریخ انتشار 2011