Flock house virus: down-regulation of subgenomic RNA3 synthesis does not involve coat protein and is targeted to synthesis of its positive

Flock house virus is a small insect virus with a bipartite RNA genome consisting ofRNA1 and RNA2. RNA3 is a subgenomic element encoded by RNA1, the genomic segment required for viral RNA synthesis (T. M. Gallagher, P. D. Friesen, and R. R. Rueckert, J. Virol. 46:481-489, 1983). Synthesis of RNA3 is strongly inhibited by RNA2, the gene for viral coat protein. Evidence that coat protein is not the regulatory element was obtained by using a defective interfering RNA2 which was messenger inactive. It was also found that RNA2 selectively down-regulated synthesis of positive-strand RNA3 but not of its complementary negative strand. cDNA-generated RNA2 transcripts, carrying four extra nonviral bases at the 3 ' end, failed to repress synthesis of RNA3 but recovered this activity after a single passage in Drosophila cells in the presence of RNA1, suggesting that down-regulation of RNA3 synthesis is controlled by competition with RNA2 for viral replicase. Nodaviruses are a family of small insect viruses with a messenger-sense bipartite RNA genome (for a review, see reference 19). Members include at least four serotypes represented by Nodamura virus (35), black beetle virus (13, 23), flock house virus (FHV) (7), and Boolarra virus (29). The genome of FHV consists of 4,506 bases split betwee