Alphavirus minus-strand synthesis and persistence in mouse embryo fibroblasts derived from mice lacking RNase L and protein kinase R

We report our studies to probe the possible role of the host response to double-stranded RNA in cessation of alphavirus minus-strand synthesis. Mouse embryo fibroblasts (MEF) from Mx1-deficient mice that also lack either the protein kinase R (PKR) or the latent RNase L or both PKR and RNase L were screened. In RNase L-deficient but not wild-type or PKR-deficient MEF, there was continuous synthesis of minus-strand templates and the formation of new replication complexes producing viral plus strands. Inhibiting translation caused minus-strand synthesis to stop and a loss of transcription activity of the mature replication complexes. This turnover of replication complexes that were stable in cells containing RNase L suggested that RNase L plays some role, albeit possibly indirect, in the formation of stable replication complexes during alphavirus infection. In addition, confluent monolayers of RNase L-deficient murine cells readily established persistent infections and were not killed. This phenotype is contrary to what has been observed for infection in vertebrate cells with a presumably functional RNase L gene and more resembled alphavirus replication in Aedes mosquito cells, in which the activity of replication complexes making plus stands was also found to decay with inhibition of translation.