RNAi is an effective tool to phenocopy the loss of function of many genes in a variety of organisms, including C. elegans (1). During an RNAi-based screen using germline-enriched RNAs (2), we found that a pool of eight dsRNAs that included
glp-1 dsRNA produced viable embryos (0-2% lethality), yet injecting the
glp-1 dsRNA alone produced a high degree of embryonic lethality (87-97%). These results might either be explained by non-specific suppression of
glp-1 (RNAi) by multiple dsRNAs, or by specific suppression by a single dsRNA. To distinguish between these possibilities,
glp-1 dsRNA was co-injected with specific members of the pool. We found that only one dsRNA from the pool could suppress
glp-1 dsRNA-mediated lethality. Additionally, removing this suppressing dsRNA from the pool of eight restored a highly penetrant
glp-1 phenotype. We were surprised to find that the suppression effect was not a suppression of
glp-1 loss of function, since two
glp-1 alleles (
q224 and
q231 ) could not be suppressed; rather it appeared to be a suppression of the RNAi process itself, since co-injection could also suppress the lethality produced by other dsRNAs (
mom-2 ,
par-2 , or
hmp-2 ). Since these results suggest that components of RNAi can themselves be targets of the RNAi machinery, we next asked whether known components of the RNAi machinery (3) could behave similarly. RNAi of either
mut-7 or
rde-1 could also suppress the lethality produced by RNAi of essential genes. The effect appears specific since unrelated dsRNAs, even at 10-fold concentrations, could not suppress this lethality. These results suggest it is possible to identify genes with roles in the RNAi pathway using RNAi. We will discuss our results and present data on a second dsRNA that also can suppress RNAi. We are currently testing candidate components of the RNAi machinery by this method, and we are developing tools for a large-scale screen to find additional components. 1. Fire et al. (1998) Nature 391:806-11 2. Reinke et al. (2001) Proc Natl Acad Sci USA 98:218-23 3. Ketting et al (1999) Cell 99:133-41; Tabara et al (1999) Cell 99:123-32