The objective of this research is to study chemical mutagenesis at the DNA level in mammals and to evaluate genetic and biochemical events in certain mutants as models of human genetic diseases. One major problem is that the level and specificity of the mutagenic response is very different between organisms. Some of this variation may be due to the genetic diversity of markers; a single (constant) sequence needs to be used as a target (indicator) in the various organisms and tissues. Our analysis is based on variance between single copies of the phi X 174 virus containing am3 and cs70 mutations. The experimental approaches and accomplishments are as follows. 1) The mutability of the phi X markers during replication in bacteria has been demonstrated. 2) Incorporated phi X DNA has been recovered from nuclear DNA of cultured mouse L-cells and, most important, viable phages have been rescued in sufficient numbers for mutagenesis studies to be practical in cell cultures or tissues of transgenic mice. 3) The phi X recovery technique does not appear to induce new mutations. 4) The conditions for mutagenic treatment of L-cell cultures have been determined and a test panel of mutagens selected. 5) The collection of mutation data from tissue cultures is in progress. An approach using an integrated viral vector in transgenic mice can combine a theoretical study of mechanism of mutation across several model organisms with the applied need for assessing mutagenic hazard. This DNA sequence can be exposed and analyzed: 1) as naked DNA (single stranded and double stranded), 2) as a single stranded virus particle, 3) double stranded in bacteria, and 4) as vector DNA incorporated into the nuclear genome of cell cultures or transgenic mice (allowing tissue-specific study of mutagenic action).
