Recent studies is Escherichia coli have shown that not all spontaneous mutations occur randomly, but that instead that some mutations are induced by selection, i.e. they are "directed" by the environment. The objective of this proposal are to understand the origins of directed mutations, the relationship between directed mutations and selection or environmental stress, the molecular and physiological basis of directed mutations, and ultimately to evauluate the importance and role of directed mutations in evolution. The achieve those objectives I shall characterize directed mutations in a variety of gene systems in Escherichia coli. The first goal will be to describe the empirical "rules" that appear to govern the appearance of directed mutations. Using that information, the next goal will be to elucidate the molecular and cellular mechanisms that are responsible for directed mutations. Directed mutations have only been detected in rather old colonies under conditions of nutritional and cellular stress. A major effort will be devoted to physiological studies of aged colonies in an effort to elucidate the relationship between cellular stress, environmental conditions, and directed adaptive mutations. These studies will employ the approaches of classical microbial genetics together with modern molecular techniques for direct examination of the DNA. The ultimate goal of these studies is to understand how directed mutations contribute to evolutionary processes, and to assess their importance in generating evolutionary diversity, particularly adaptive diversity.
