In a genetic screen for genes involved in the cellular response of C. elegans to the PFT Cry5B, we found a mutant predicted to be defective in protein N-glycosylation in the ER (L.J.B. and R.V.A., manuscript in preparation). Since defects in protein glycosylation induce the UPR, this result suggested that perhaps the UPR might play a role in protection against PFTs. To test this hypothesis, we first investigated whether or not the UPR was activated by a PFT. The xbp-1 gene is spliced upon activation of the IRE-1 branch of the UPR, and its splicing is one marker for IRE-1 (and UPR) activation [13] . In C. elegans, the xbp-1 intron spliced by IRE-1 is 23 nucleotides and the induction of this splicing event can be detected by RT-PCR [14] . To analyze xbp-1 mRNA transcript splicing, animals were fed Escherichia coli expressing Cry5B and compared to worms fed control E. coli ( Figure 1A ). While there is abundant unspliced xbp-1 mRNA transcript in both samples, there is an increase in the spliced xbp-1 transcript from worms ingesting Cry5B, indicating activation of the IRE-1 pathway. Quantitative analyses indicate that the xbp-1 spliced transcript increases 2.3, 3.0, and 3.0 fold at the 7, 8, and 9 h time points respectively.