The Hsp83 maternal promoter governs expression of a Tag:MCP-EGFP fusion protein flanked by α-tubulin 3'UTR and genomic sequences. A Tag:NLS(SV40-largeT) nuclear localization signal is present at the N-terminal end of the open reading frame. 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 fusion protein is targeted to the nucleus due to the presence of the Tag:NLS(SV40-largeT) tag.