A stem-loop "kissing" model for the initiation of recombination and the origin of introns |
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Authors: | Forsdyke DR |
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Institution: | Department of Biochemistry, Queen's University, Kingston, Ontario, Canada. |
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Abstract: | Mutations which improve the efficiency of recombination should affect
either the proteins which mediate recombination or their substrate, DNA
itself. The former mutations would be localized to a few sites. The latter
would be dispersed. Studies of hybridization between RNA molecules have
suggested that recombination may be initiated by a homology search
involving the "kissing" of the tips of stem loops. This predicts that, in
the absence of other constraints, mutations which assist the formation of
stem loops would be favored. From comparisons of the folding of normal and
shuffled DNA sequences, I present evidence for an evolutionary selection
pressure to distribute stem loops generally throughout genomes. I propose
that this early pressure came into conflict with later local pressures to
impose information concerning specific function. The conflict was
accommodated by permitting sections of DNA concerned with a specific
function to evolve in dispersed segments. Traces of the conflict seem to be
present in some modern intron-containing genes. Thus, introns may have
allowed the interspersing of selectively advantageous stem loops in coding
regions of DNA.
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