Novel Drosophila Viruses Encode Host-Specific Suppressors of RNAi
(A) Schematic representation of the genome organization of Nora virus. The virus encodes four open reading frames, some of which have a slight overlap. (B) Phylogenetic analysis of the most conserved Nora virus gene (VP4) suggests that the three Drosophila Nora-like viruses are each other's closest relatives, and that they are all closely related to the Nora-like sequence derived from Haematobia irritans. Although DimmNV appears to be most closely related to DmelNV based on VP4, the extreme divergence from the other Nora-like sequences may make the rooting unreliable. The tree presented is the mid-point rooted Bayesian maximum a posteriori tree (99% of the posterior set), the topology of which is identical to a Maximum Likelihood (ML) tree. Support values are given for internal nodes (Bayesian posteriors/ML bootstraps). The scale bar represents 0.5 amino acid substitutions per site. (C) A sliding-window analysis of nonsynonymous divergence between the three Drosophila Nora viruses, calculated as the number of nonsynonymous substitutions per nonsynonymous site. Dashed lines show a nominal 95% significance threshold for genome-wide peaks in divergence derived from randomisation tests, such that peaks crossing the lines are unlikely to occur by chance, given the overall divergence for that virus (colours correspond to the three viral lineages). Insets for each viral protein are unrooted trees with branch lengths proportional to overall divergence for that gene.