To reduce, rather than completely abrogate expression, we designed retroviral shRNA constructs directed against Prmt5. Two lentiviral constructs, sh-Prmt5-1 and sh-Prmt5-2, were stably introduced into primary MEFs, with >80% of cells surviving 48 h after viral infection and selection for shRNA expression (data not shown). This evidence concerns the gene PRMT5 and viral infectious disease.