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Abstract

The RNA phage fr induces in Escherichia coli cells the production of double stranded RNA, which is identified by its thermal denaturation profile ( Tm 101 °C in 0,2-m. Na⊕ ), by its nonreactivity with formaldehyde and by its buoyant density in Cs2SO4 (1,609 g cm-3 , compared to that of fr-RNA = 1,634 g cm-3 ). Unless denatured the double strand is resistant to RNase. In its high molecular weight form the double stranded R N A has twice the weight of fr-RNA, as estimated from the sedimentation coefficient (s20 = 14,5). The base ratios are those expected for a double stranded replicative from of fr-RNA. By melting and annealing one of the strands of the non-radioactive material can be exchanged for 32P-fr-RNA from phage particles. Infectiosity of the doublestranded RNAhas not yet been shown. Extracts from infected cells contain double strand bound to the 30 - 50 s fraction; there is also double strand in the supernatant, apparently in the form of relatively low molecular weight fragments. The double stranded RNA, isolated at the height of infection, accounts for 3 - 8% of the cellular RNA. Cells infected with 32P-fr show a surprisingly large part of the infecting RNA bound to ribosomes quite late in the latent phase. The meaning of this result is discussed.