With the exception of NUP57, RNA15, SPC29 and YGR251w, each of the essential genes identified in this study have recognized orthologs in Arabidopsis thaliana (http://www.arabidopsis.org/ and Figure 3 . Dox-induced repression of five essential yeast genes inhibits BMV RNA replication. Total RNA extracts were obtained from wild type R1158 and untreated and dox-treated (10 mg/ml) essential yeast strains expressing BMV 1a, 2a Pol and RNA3. Accumulation of positive-and negative-strand RNA3 and subgenomic RNA4 was detected by Northern blotting using probes specific for BMV RNA3 and RNA4. Equal loading of total RNA was verified by probing for 18S rRNA. Values represent the mean of four independent experiments. doi:10.1371/journal.pone.0023988.g003 Table 5 . Essential genes whose repression was confirmed to inhibit BMV RNA accumulation in secondary validation testing. [66, 67] . Similarly, PRE1 (PBD1 and PBD2 in Arabidopsis) and RPT6 (RPT6a and RPT6b in Arabidopsis) are essential components of the highly conserved 26S proteasome and recent results from our laboratory show that BMV RNA replication in yeast and plant cells depends critically on the ubiquitin-proteasome pathway (B. Gancarz and P. Ahlquist, unpublished results) [9, 68] .