UASt regulatory sequences drive expression of the full-length Xbp1 transcription unit (includes the 5' UTR, coding sequence and intron, 3' UTR and 0.55kb immediately downstream of the 3'UTR). Sequence encoding EGFP has been inserted at the C-terminal end of the coding region. The EGFP tag only becomes in frame with the Xbp1(s) coding sequence after splicing using the unconventional splice site (this occurs under stress conditions).