This invention relates to the field of biotechnology or genetic engineering.Specifically, this invention relates to the field of gene expression. Morespecifically, this invention relates to novel substitution mutant receptorsand their use in a nuclear receptor-based inducible gene expression system andmethods of modulating the expression of a gene in a host cell for applicationssuch as gene therapy, large scale production of proteins and antibodies, cell-based high throughput screening assays, functional genomics and regulation oftraits in transgenic organisms.