Reliance of on High Rates of Host Proteolysis Revealed by a Genome-Wide RNAi Screen of Cells.

are gram-negative, obligate, intracellular bacteria carried by a majority of insect species worldwide. Here we use a -infected cell line and genome-wide RNA interference (RNAi) screening to identify host factors that influence titer. By screening an RNAi library targeting 15,699 transcribed host genes, we identified 36 candidate genes that dramatically reduced titer and 41 that increased titer. Host gene knockdowns that reduced titer spanned a broad array of biological pathways including genes that influenced mitochondrial function and lipid metabolism. In addition, knockdown of seven genes in the host ubiquitin and proteolysis pathways significantly reduced titer. To test the relevance of these results, we found that drug and mutant inhibition of proteolysis reduced levels of in the oocyte. The presence of in either cell lines or oocytes dramatically alters the distribution and abundance of ubiquitinated proteins. Functional studies revealed that maintenance of titer relies on an intact host Endoplasmic Reticulum (ER)-associated protein degradation pathway (ERAD). Accordingly, electron microscopy studies demonstrated that is intimately associated with the host ER and dramatically alters the morphology of this organelle. Given lack essential amino acid biosynthetic pathways, the reliance of on high rates of host proteolysis via ubiquitination and the ERAD pathways may be a key mechanism for provisioning with amino acids. In addition, the reliance of on the ERAD pathway and disruption of ER morphology suggests a previously unsuspected mechanism for ' potent ability to prevent RNA virus replication.