Steen writes:
Well, the nylon bug was DOCUMENTED to have a frameshift mutation that lead to completely new traits.
Is this actually the case? Certainly the
Ohno (1984) paper makes a convincing argument that the existence of an alternative 400+ amino acid sequence coding ORF which would be formed by the removal of a single nucleotide which forms a termination codon in that longer ORF.
As I say, the argument is convincing but is it a documented frameshift mutation? Is there a plasmid or a gene identified in the wild corresponding to the alternative long ORF?
One site which discusses the frame-shift origin is
here, I dont know if this is a site you've seen or where you got your information concerning the fame-shift from but this site is one I have often seen referenced for this claim. The site says...
Detailed examination of the DNA sequences of the original bacterium and of the nylon-ingesting version show identical versions in the gene for a key metabolic enzyme, with only one difference in over 400 nucleotides.
And yet the Ohno paper I mentioned previously says in its conclusions...
Indeed, the very basic former totally lacking Trp and Asn residues is not likely to function as an enzyme of any sort,
And produces absoloutely no comparison with any
original plasmid sequence but rather a
hypothetical alternative open reading frame. If this is the source of the 'Detailed examination' showing only 'one difference in over 400 nucleotides' then it is a phantasm caused by a misreading of the original paper.
I want to make clear that I have no reason to doubt that this is most likely how the nylon digesting genes have arisen, I just don't know if you could say that it is really a
documented case of a frameshift mutation leading to a new trait.
It may just be that there is subsequent research of which I am unaware which has identified an ancestral form of teh gene with the alternative ORF still functional, if so I would be obliged if someone could provide it.
TTFN,
WK
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