Research in molecular genetic studies and in transgenic biotechnology has resulted in excellent advancements in exploiting gene transfer techniques. Basic research in transcriptional and/or translational control, protein engineering, cellular immunological mechanisms, and developmental genetic processes using transient or stable transgenic approaches have generated the main body of information in our current understanding of various molecular biology and cell biology disciplines. Parallel with this development, the gene transfer and transgene expression techniques have also been extremely useful in their application to plant and animal (including mammalian) biotechnologies. Specifically, analyses of promoter activity and usage have played important roles in generation of genetically engineered plants, transgenic animals, and recombinant or transgenic protein products in various microbial fermenters or plants or in mammalian cell bioreactors. More recently, various gene transfer and promoter usage technologies have also been evaluated extensively for application to gene therapy research.