exons & protein domains
arlin at is.dal.ca
Fri Jul 19 18:47:03 EST 1996
R M Bernstein wrote:
> hi bob,
> these are theories perhaps suggested by crick himself (prediction of rna
> world and all that it implies), and since championed by gilbert and more
> recently wf doolittle-and others.
. . .
> all errors in the story above are open to correction/clarification
The history of speculation about introns following their discovery in 1977
is actually a bit different, and is not so much owing to Crick as implied
1977 - many authors speculate that introns are "good" for something, such as
chromosome structure or gene regulation.
1978 - Gilbert (Nature 271, 501) gathers together diverse ideas to the effect
that introns are beneficial and that their "role" is to speed evolution
by various means including developmental gene rearrangements [this
is the idea that is now called "exon shuffling"].
1978 - Darnell (Science 202, 1257) and Doolittle (Nature 272, 581) suggest
that split genes might predate eukaryotes, and go even further
to suggest that they might represent a primordial form of gene
organization that predates even a eukaryote-prokaryote ancestor.
1978 - Blake (Nature 273, 267) suggests that the modularity of split genes may
reflect the modularity of proteins, such that ancient exon shuffling may
explain such observations as the recurrence a nucleotide-binding module
in different (ancient) dehydrogenase enzymes.
1979 - Crick (Science 204, 264) considers quite a wide array of possibilities,
and makes the novel suggestion that introns may operate similarly to
bacterial insertion sequences in creating a small target-site
Although Crick's paper was arguably the most lucid of these, the priority for
exon shuffling goes to Gilbert, the priority for introns-early is shared by
Darnell and Doolittle, and the priority for the idea that exons encode
structural modules goes to Blake. It is not clear who gets the priority for
the idea of introns as transposable elements that insert into genes. Both
Crick and Cavalier-Smith cite their own (separate) papers from 1978 in this
regard, and these are papers I have not yet seen.
> goal. functional domains- as defined not only by exons that encode a
> "functional" area of a protein, but that are separated by introns from other
> exons, and not themselves interrupted- do indeed exist
Do exons coincide with some protein domains just by chance, or is there a
statistically significant correlation? Does this apply to ancient proteins
as well as to recently evolved ones?
Department of Biochemistry
Halifax, Nova Scotia B3H 4H7 CANADA
(email) arlin at is.dal.ca
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