Spontaneous mutation rates have been assumed to be constant and uninfluenced by selective forces. Recent experiments have shown, however, that when stationary cells of Escherichia coli are subjected to certain non-lethal selections, mutants appear with time. Because the only mutants that accumulate among the population are those that are selected for this phenomenon has come to be known as "directed" or "adaptive" mutation. This phenomenon is not due to obvious artifacts and is under genetic control. This research will investigate the cellular process that give rise to "directed" mutations. Using a well-defined mutational assay, the involvement of recombination, DNA synthesis, and various DNA repair pathways will be investigated. New genetic defects affecting the process will be isolated. That populations are able to increase their variability under stress without deleterious genetics consequences has clear evolutionary significance. %%% Understanding the mechanism by which this is accomplished may lead to new insights into the regulation of genetic processes and how they may be influenced by the physiology of nutritionally-deprived cells.
