To systematically identify novel, essential host genes affecting BMV RNA replication, we screened a dox-repressible library of essential yeast strains [27] . This collection contains ,900 yeast strains, each with a single endogenous essential gene promoter replaced by a tetracycline-repressible promoter [27] . Upon the addition of the tetracycline derivative dox to growth media, expression of the essential gene is repressed, and the protein depleted. This library was used to identify changes in BMV RNA replication after repression (dox-treated) relative to continuous expression (untreated) of a specific essential host gene.