Shuffling, Recombination, and the Importance of ...Nonsense
|Although DNA holds the instructions for making proteins, a sizable fraction of these sacred codes appears to contain nonsense. Indeed, after an RNA copy of DNA is made, an elaborate splicing system removes the genetic junk, sequences called introns. The substantive information in the remaining codes, called exons, can be patched together and translated into an enzyme or other useful protein. So why do introns exist at all?
A report in the June 22  Biochemistry may provides a clue. Using a chemical probe, two chemists at the California Institute of Technology in Pasadena have discovered a structural landmark that appears to flag introns.
Here we have what I think is a first indication that introns are structurally delineated at the DNA level, says Jacqueline K. Baron, one of the Caltech researchers.
A regularly occurring structure on DNA should play some important role, she says. Thus, the finding contradicts the view that introns are evolutionary relics that are removed because they serve no purpose.
The work supports the exon shuffling theory, which contends that introns act as spacers where breaks for genetic recombination occur. Under this scenario, exons---which usually contain instructions for building a protein subunit---remain intact when shuffled during recombination. In this way, proteins with new functional repertoires can evolve .
[In other words, the breaks in the chromosomes can be made in the introns, the filler sections, which are marked so as not to be confused with the exons, the sections containing important genetic information. In this way, the breaks never occur in the middle of genes, but only in the marked filler material, thus enabling the gene sequences to be duplicated correctly. Nonsense sets off sense, making it easier to identify.]
---from an article by K.F. Schmidt, Science News, July 10, 1993, p. 21. Not the original title given. comments (in other words...) are my own interpolations.
can there be special information disguised in what appears to be an introns?
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