RNA silencing processes result in the sequence-specific degradation of RNA and effective post-transcriptional gene silencing. In the May 17 Science, Hongwei Li and colleagues from the University of California, Riverside report that Flock House Virus (FHV) is both an initiator and a target of RNA silencing (Science 2002, 296:1319-1321).

Li et al. observed that B2 gene of FHV resembles a plant virus gene encoding a silencing suppressor. Expression of the FHV B2 protein in plants prevented RNA silencing of a GFP transgene. FHV normally infects vertebrate and invertebrate animal hosts. They found that infection of Drosophila cells resulted in the production of FHV short-interfering RNA (siRNA). The RNA silencing machinery prevented FHV accumulation, indicating the FHV is also a target of RNA silencing. The FHV B2 protein suppresses RNA silencing and favors FHV accumulation.

These results provide evidence that RNA silencing is part of the innate...