UASt regulatory sequences drive expression of the 'ERK-KTR' kinase translocation reporter of MAPK activity (PMID:24949979). 'ERK-KTR' is a fusion protein composed of the ERK docking site from the Mmus\Elk1 gene, a nuclear localization signal (NLS), a nuclear export signal (NES) and the Clover fluorescent protein (sequences codon-optimized for Drosophila). Both the NLS and NES have been mutated to contain consensus phosphorylation sites for MAPK, such that phosphorylation decreases the activity of the NLS and increases the activity of the NES. This results in the protein shuttling from the nucleus to the cytoplasm in response to MAPK phosphorylation.