Promotion of evolution by intracellular coexistence of mutator and normal DNA polymerases

The efficient evolution of a population requires both genetic diversity and stable reproduction of advantageous genotypes. The accuracy of DNA replica tion guarantees the stable reproduction, while errors during DNA replicatio n produce the genetic diversity. Thus, one key to the promotion of evolutio n is inherent in DNA replication. In bacteria, replication forks progress b idirectionally from the single origin of replication on a genome. One repli cation fork contains two DNA polymerase molecules so that four DNA polymera ses simultaneously carry out the replication of a genome. It is generally b elieved that the fidelity of the intracellular DNA polymerases is identical (parity strategy). To test this, we examined the effects of the intracellu lar coexistence of a mutator polymerase with low fidelity and a normal poly merase with high fidelity on adaptive evolution (disparity strategy). From the analysis using genetic algorithms based on the bacterial replication, i t was found that the population using the disparity strategy could further expand its genetic diversity and preserve the advantageous genotypes more p rofoundly than the parity population. This strongly suggests that bacteria replicating with a disparity strategy may undergo rapid evolution, particul arly during severe environmental changes. The implications of the conspicuo us adaptability of Escherichia coil mutator strains are discussed in this c ontext. (C) 2001 Academic Press.