Natural evolution adaptive mutations

There is some evidence to support the notion that rapid adaptation of function is better achieved by having access to more nonconservative amino-acid substitutions. Still, point mutation methods such as error-prone PCR remain most suitable for attempts to mimic natural evolution or to retrace history. Further functional adaptation may be achieved by saturation mutagenesis at sites identified during random mutagenesis experiments (Miyazaki et al., 1999). 

The number of thermally adaptive mutations resulting from directed evolution studies is too small at present to support a detailed statistical analysis. Here we summarize some properties of the mutations discovered in the studies reviewed above, and compare them to the amino-acid differences seen among naturally occurring enzymes that have adapted to different temperatures. Lists of the amino-acid substitutions discovered... 

In addition to mutation rate, even the other molecular parameters turned out to be different from the expectations of selectionism. It was discovered, for example, that neutral mutations are not in the least a tiny minority with respect to adaptive mutations, and the actual ratio is probably the other way round. At the molecular level, in other words, the dominant mechanism of evolution is not natural selection but genetic drift, and this led Motoo Kimura to formulate the neutral theory of molecular evolution (1968, 1983). 

A fine balance must be maintained between the need to create and enhance the diversity and to minimise the damage caused by loss of information. In natural evolution, mutation rates which are very low lead to only gradual change in the characteristics of a population, and it may then be unable to adapt with sufficient speed to changes in the environment. At the other extreme, high mutation rates cause destruction of information and the risk that new individuals may not be viable because of the loss of vital genetic data. The optimum conditions for evolution in both natural and artificial systems seem to be those in which mutations occur at a rate which is just below that at which significant amounts of information are lost. 

Many clues as to how to engineer better enzymes came from drawing parallel comparisons with nature and studying how nature has created authentic enzymes. By studying the evolution of bona fide proteins, it has been learned that they are hi ly adaptable, incessantly changing molecules. They can sometimes acclimatize to different environments and can even adopt unique functions, at least over evolutionary time scales. It is now known that the natural processes of mutation, recombination and se lection resulted in the creation of enzymes with varied functions through the evolution of a common ancestral protein of the same general structure (16),... 

Kimura s theory has not been universally accepted, and the debate between selectionism and neutralism is still going on, but the experimental data have changed for good our view of molecular evolution. Today, biologists are aware that neutral mutations are a fact of life, and that genetic drift is, at the molecular level, at least as important, if not more important, than natural selection. It must also be noticed that this does not diminish in the least the key role of natural selection in phenotypic evolution, and Kimura himself explicitely acknowledged that The basic mechanism of adaptive evolution is without doubt natural selection. He added however that Underneath the remarkable procession of life and indeed deep down... 

Wiley, Chichester (Novartis Found Symp 223) p 260-275 Rice WR1988 Heritable variation in fitness as a prerequisite for adaptive female choice the effect of mutation-selection balance. Evolution 42 817-820 Rose M, Charlesworth B 1980 A test of evolutionary theories of senescence. Nature 287 141—142 Rushton JP 1995 Race, evolution, and behavior a life history perspective. Transaction, New Brunswick, NJ... 

Traditionally, the framework of evolution in life works through two aspects of organization, the genotype and the phenotype. The genotype is the heritable information encoded in the DNA, which is translated through the RNA molecules into proteins. The phenotype is valuable for adaptation and at the molecular level plays a key role in natural selection. One conventionally assumes that a selection of phenotypes leads to an enhancement in the numbers of the genotype. Furthermore, mutations of the genotype lead to the possibility of new phenotypes. 

The strategy nature uses to adapt organisms to new demands is evolution. According to Darwinian theory, the fantastic diversity of life was created by random mutation and natural selection111. The power and simplicity of the evolution... 

In many instances, naturally occurring (so-called wild-type ) enzymes show very high efficiency and selectivity for certain substrates, but not necessarily for the ones of particular interest from a synthetic point of view. In the directed evolution approach, enzymes are adapted to a given task by mutation on the DNA level (mostly by error prone PCR, epPCR, or by gene... 

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