Ectopic gene expression is an important tool for gene analysis and protein science, offering insight into gene function at multiple levels. Gain-of-function experiments often result in phenotypic changes which can provide the counterpart to loss-of-function studies, such as gene knockdown.

Gene expression constructs, such as cDNAs and ORFs, are commonly used to over-express a protein of interest to be analyzed for effect on cellular phenotype, intracellular localization, or for the isolation and purification of a protein for further study.

This schematic demonstrates a gene expression construct being translated and expressed in a eukaryotic cell. Once in the nucleus, the cellular machinery recognizes the promoter, transcribes the protein coding sequence into mRNA and translates the protein. The resulting gene product can cause alterations in phenotype, be purified for further processing or to be tracked via localization to better understand protein function.