The long-term objective of this study is to acquire a greater understanding of the mechanisms of spontaneous mutagenesis as they occur in cells. Directly related to the creation of mutations is the fidelity mechanisms that cells employ to keep mutational events at a low level of occurrence. The list of human diseases and disorders that are affected by mutational events is extensive and ranges from the so-called single gene genetic disorders to multifactorial conditions that come about via the combined effects of environmental factors and multiple mutational events that occur to achieve the altered phenotype. Even infectious diseases once thought to be almost exclusively environmental in nature are now known to be influenced by the genotype of both the host and the pathogen. Somatic mutations give rise to the variety of human cancers. While great attention has been given to mutational events caused by environmental chemical mutagens, it is likely that most mutational events that occur in human populations are spontaneous in nature. [unreadable] [unreadable] A direct approach to study mechanisms of spontaneous mutagenesis is to characterize mutant alleles, called antimutator alleles that cause decreases in spontaneous mutation frequencies. This is possible with the genetically well-characterized bacterium, Escherichia coli. A series of suspected or partially characterized antimutator alleles will be fully tested and characterized with the goal of revealing mutagenic pathways. Since such pathways and the fidelity mechanisms that keep mutational events at a low frequency are well conserved, it is expected that results obtained from this bacterial study would be applicable to other organisms, including humans. [unreadable] [unreadable] For the past several years, many studies have collectively shown that spontaneous mutations occur in starving or stressed bacterial cells. Some of these mutations are caused by the action of a group of specialized DNA polymerases that are capable of synthesizing past damaged or unusual DNA templates. In E. coli it has been shown that one or more of these polymerases may be active in starving/stressed cells where apparently the synthesis past a damaged template comes at a "cost" of creating mutations. The present application intends to more fully characterize the creation of mutations under these physiological conditions. Humans possess a number of these specialized DNA polymerases whose activities may be responsible for a significant portion of the human mutational load. [unreadable] [unreadable]