The intent is to design retrovirus vectors to a) study retrovirus replication, b) optimize the efficiency and usefulness of gene transfer, and c) study cis-acting elements that regulate gene expression. The principle vector will be a derivative of mouse amphotropic virus 4070 to maximize host range and allow efficient gene transfer and expression in human cells. The system will be designed to eliminate the need for a helper virsus or phenotypic selection and will not require the synthesis of any viral proteins or RNA in the target cells. The methodologies involved include recombinant DNA cloning, in vitro mutagenesis of DNA, growth of virus in tissue culture, and analysis of gene expression using gel electrophoresis and nucleic acid hybridization. The long term goals are a) to better understand retrovirus replication and pathogenesis, b) to understand the regulation of gene expression, and c) to develop a gene transfer system that will be useful in both somatic cell and germline-directed gene transfer. The health-relatedness of the project will stem from its potential usage in gene therapy. A more complete understanding of retrovirus replication and expression will increase our understanding of oncogenesis.