22nd IUBMB & 37th FEBS Congress, Sevilla 2012

Congresos de la SEBBM

Evolving molecules, viroids, and viruses – Theory, models, and reality

Peter Schuster

  • Universitaet Wien, Austria

Evolution in nature is an exceedingly complex process involving not only the species under consideration
but also all other components of the entire ecosystem. Elimination of unnecessary complications and
simplification through keeping variable environmental factors constant in the spirit of physics allows for
the reduction to molecular systems that show features, which are characteristic of Darwinian evolution
and which can be modeled and analyzed by the conventional methods of physics and chemistry.
Evolution through mutation and selection is modeled by a mechanism based on chemical kinetics of
correct and error-prone replication as parallel reaction channels. This molecular theory of evolution is
readily extended to high mutation rates as they are occurring, for example, with viroid and virus
populations. The major result of the theoretical analysis is the existence of a sharply defined threshold
value for the mutation rate, called error threshold, above which error accumulation results in
breakdown of inheritance and extinction of the population. Depending on the fraction of lethal
mutations, population may die out by two mechanisms: (i) crossing the error threshold and continued
production of too many highly mutated variants with low fitness and (ii) direct accumulation of lethal
variants that are unable to reproduce. Lethal mutagenesis is of great importance for the development of
novel therapeutic strategies against viruses. Evolution of molecules has been applied to the design of
molecules with predetermined functions and gave rise to the new discipline of evolutionary
biotechnology. Systematic work on the measurement of distributions of sequences and fitness values in
populations of molecules and viruses, which is based on the application of modern ‘omics’ techniques,
provided experimental insight into fitness landscapes and is accessible now as a new and solid basis for
an elaborate and quantitative molecular theory of evolution.

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