PATTERN GENERATION IN MOLECULAR EVOLUTION - EXPLOITATION OF THE VARIATION IN RNA LANDSCAPES

Evolution of RNA secondary structure is studied using simulation techn iques and statistical analysis of fitness landscapes. The transition f rom RNA sequence to RNA secondary structure leads to fitness landscape s that have local variations in their ''ruggedness.'' Evolution exploi ts these variations. In stable environments it moves the quasispecies toward relatively ''flat'' peaks, where not only the master sequence b ut also its mutants have a high fitness. In a rapidly changing environ ment, the situation is reversed; evolution moves the quasispecies to a region where the correlation between secondary structures of ''neighb oring'' RNA sequences is relatively low. In selection for simple secon dary structures the movement toward flat peaks leads to pattern genera tion in the RNA sequences. Patterns are generated at the level of poly nucleotide frequencies and the distribution of purines and pyrimidines . The patterns increase the modularity of the sequence. They thereby p revent the formation of alternative secondary structures after mutatio ns. The movement of the quasispecies toward relatively rugged parts of the landscape results in pattern generation at the level of the RNA s econdary structure. The base-pairing frequency of the sequences increa ses. The patterns that are generated in the RNA sequences and the RNA secondary structures are not directly selected for and can be regarded as a side effect of the evolutionary dynamics of the system.