Differentiation between Broccoli Necrotic Yellows Virus and Lettuce Necrotic Yellows Virus by their Transeriptase Activities

An endogenous RNA-dependent RNA polymerase has been demonstrated in broccoli necrotic yellows virus (BNYV) particles. The enzyme requires a temperature of 26 °C, a pH value of 7.5, 0.5 % NP40 and 4 mM-Mg 2+ for maximum synthesis of RNA; Mn 2+ inhibited the activity. Addition of EDTA to the reaction mixture did not stimulate the activity in the presence of higher amounts of Mg 2+. The in vitro transcription products of BNYV hybridized to the virus genome, but not to that of lettuce necrotic yellows virus (LNYV). The transcriptase activity was abolished by centrifugation a glycerol gradient after treating the virus with NP40 in a high salt solution; combining the pellet and the upper part of the gradient restored the activity. Cross-complementation of BNYV and LNYV transcription could not be obtained by heterologous combination of the pellet and supernatant fractions of the two viruses