UAS regulatory sequences drive expression of a chimeric construct in which EGFP is fused after the 252nd amino-acid residue (i.e. after the putative Ire1 splice site) of the Xbp1-RA isoform. Thus, EGFP is in frame with Xbp1 only after the 23-base stem-loop of Xbp1 is eliminated by splicing.