To identify mechanisms and cellular functions that limit expression of SKN-1 targets in the absence of stress, RNAi was used to screen for genes that prevent the Phase 2 gene
gcs-1 from being active constitutively in the intestine. In the intestine
gcs-1 is expressed at low levels under normal conditions, and is upregulated dramatically by oxidative stress. This regulation can be visualized using a reporter in which the
gcs-1 promoter drives expression of the green fluorescent protein (GFP) gene (
gcs-1p::GFP). Two rounds of screening confirmed 37 positive genes for which RNAi resulted in robust and consistent expression of gcs- 1::GFP in the intestine.