A function for ABC transporters in RNAi

Dissertation (Ph.D.)--University of Kansas, Molecular Biosciences, 2007.RNA interference (RNAi) is a conserved gene-silencing phenomenon that can be triggered by delivery of double stranded RNA (dsRNA) to cells and is a widely exploited technology in analyses of gene function. While a number of proteins that facilitate RNAi have been identified, current descriptions of RNAi and interrelated mechanisms are far from complete. Here we report that the Caenorhabditis elegans gene haf-6 is required for efficient RNAi. HAF-6 is a member of the ATP binding Cassette (ABC) transporter gene super family. ABC transporters utilize ATP to translocate small molecule substrates across the membranes in which they reside, often against a steep concentration gradient. Collectively, ABC transporters are involved in a variety of activities, including protective or barrier mechanisms that export drugs or toxins from cells (Broeks et al., 1996; Bauer et al., 1999; Begley, 2004; Fromm, 2004), in organellar biogenesis (Aubourg, 1994), and in mechanisms that protect against viral infection (Trowsdale et al., 1990; Abele and Tampe, 2004). HAF-6 is expressed predominantly in the intestine and germline and is localized to intracellular reticular organelles. We further demonstrate that nine additional ABC genes from diverse subfamilies are each required for efficient RNAi in C. elegans, all expressed in the germ line and may function by aiding in the formation of a functional RDE-2/MUT-7 complex. Thus, the ability to mount a robust RNAi response to dsRNA depends upon the deployment of two ancient systems that respond to environmental assaults: RNAi mechanisms and membrane transport systems that utilize ABC proteins