Production of PMMoV dsRNA in an E. coli strain deficient for RNase III. Bacteria of the indicated genotypes were transformed with either pGEM/IR 54, a plasmid designed to express a hairpin structure consisting of 977 bp of PMMoV RNA (IR 54), or with the empty plasmid (HT115). Bacterial cultures were induced with IPTG and processed for total nucleic acid. Samples were resolved by electrophoresis on 1% agarose gel before (A) or after treatment with RNase A (B), and nucleic acid was visualized by staining with ethidium bromide. DNA markers, λEcoRI-HindIII molecular weight markers; RNA markers, 100 ng of in vitro-synthesized Neo poly(A) RNA. In vitro IR 54, T7 in vitro-transcription product of pGEM/IR 54. The position of bacterially expressed IR 54 is indicated.