UASt regulatory sequences drive expression of GFP tagged with Tag:MCP and with a nuclear localization sequence (Tag:NLS(Unk)). In the presence of a mRNA tagged with Tag:MS2 (an RNA stem loop to which Tag:MCP binds), the fusion protein can bind to this tagged mRNA, allowing its localization within the cell to be studied. In the absence of a Tag:MS2-tagged mRNA (or when unbound), the GFP-Tag:MCP fusion protein will be targeted to the nucleus due to the presence of the Tag:NLS(Unk) tag.