RNA-dependent RNA polymerase activity associated with endogenous double-stranded RNA in rice

RNA-dependent RNA polymerase (RdRp) activity was detected in the crude micr osomal fraction of rice cultured cells that contain a 14 kbp double-strande d RNA (dsRNA), RdRp activity is maximal in the presence of all four nucleot ide triphosphates and Mg2+ ion and is resistant to inhibitors of DNA-depend ent RNA polymerases (actinomycin D and a-amanitin). RdRp activity increases approximately 2.5-fold in the presence of 0.5% deoxycholate, Treatment of purified microsomal fraction with proteinase K plus deoxycholate suggests t hat the RdRp enzyme complex with its own 14 kb RNA template is located in v esicles. The RdRp enzyme complex was solubilized with Nonidet P-40 and puri fied by glycerol gradient centrifugation, then exogenous RNA templates were added. Results indicate that exogenous dsRNA reduces RNA synthesis from th e endogenous 14 kb RNA template.