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le mardi 20 mai à 16:30

Erich Bornberg-Bauer (Institute for Evolution and Biodiversity, University of Muenster)

Salle de formation du PRABI - 2ème étage

par Vincent Daubin - 20 mai 2008

Phenotypic Transitions in a multi-trait landscape

A central question in molecular evolution concerns the nature of
phenotypic transitions, in particular if neutral mutations hamper
or somehow facilitate adaptability of proteins or RNAs to new
requirements.

Proteins and RNA have been found to accomplish different task by
fluctuate between different phenotypes (structures), with frequencies
and thus intensity of the associated trait being proportional to
their stability. Therefore, functional promiscuity may correspond
to different structures with energies close to the ground state which
then represent multiple selectable traits. We here postulate that
these near-ground state structures facilitate smooth transitions
between phenotypes. Using biophysical model systems with exhaustive
mappings of genotypes (sequences) onto phenotypes (structures), we
demonstrate that this is indeed possible because of a smooth gradient
of stability along which any phenotype can be optimised and also
because of mutational proximity of similar phenotypes in genotype
space.

Our model provides a rationalisation of the intriguing, and
otherwise puzzling experimental observation that adaptation to new
requirements, e.g. latent function of a promiscuous enzyme, can
proceed while the "old", phenotypically dominant function is
maintained along a series of seemingly neutral mutations.

Thus pleiotropy may facilitate adaptation of latent traits BEFORE
gene duplications and increase the effective adaptability of proteins