SUMMARYA function for mitochondria in the reproduction of Rous sarcoma virus (RSV) in chronically and newly infected chick embryo cells was studied by using chloramphenicol and ethidium bromide. Chloramphenicol (CAM) and ethidium bromide (EB) were both shown to decrease the rate of growth of infected chick embryo cells and to inhibit the synthesis of mitochondrial macromolecules. Both drugs however had little or no effect on the incorporation of labelled leucine, thymidine and uridine into total cellular macromolecules. Neither CAM (80 #g/ ml) nor EB (o'4 #g/ml) inhibited the production of infectious virus. In contrast, camptothecin, an inhibitor of cellular but not mitochondrial macromolecular synthesis, was shown to depress the production of infectious virus. The results indicate that the mitochondrial macromolecular synthesis machinery of RSVinfected chick embryo cells does not contribute to virus production.

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1. Homogenates of cultured chick embryo fibroblasts have been quantitatively fractionated by differential centrifugation. Using cytochrome c oxidase, succinate dehydrogenase, acid phosphatase and NADPH-cytochrome c reductase as marker enzymes, poly(A) hydrolase has been shown to be a mitochondrial enzyme.2. To test the biosynthetic origin of mitochondrial poly(A) hydrolase and to demonstrate its cytoplasmic site of synthesis, we have treated the cells with ethidium bromide, inhibitor of mitochondrial transcription, and chloramphenicol and cycloheximide, inhibitors of mitochondrial and cytoplasmic translations respectively. The activity of poly(A) hydrolase has been compared to that of succinate dehydrogenase, an enzyme coded for by the nuclear genome and that of cytochrome c oxidase, an enzyme coded for partly by the nuclear genome and partly by the mitochondrial genome. The results obtained indicate that in chick embryo fibroblasts poly(A) hydrolase is an enzyme coded for by the nuclear genome. Further, the hydrolase is synthesized on cytoplasmic ribosomes and has a half-life much shorter than succinate dehydrogenase and cytochrome c oxidase.Sheiness et a/. [l] have recently reported that the poly(A) attached to heterogeneous RNA appears to have the same size as the poly(A) that is initially found as messenger RNA. Soon after cytoplasmic appearance, however, the poly(A) begins to diminish in size, decreasing from about 200 nucleotides to 50 nucleotides or less [2-41. The enzyme involved in this particular cytoplasmic process is still unknown but could well be cellular poly(A) hydrolase [5-71, which catalyzes the hydrolysis of poly(A) to oligonucleotides with 3'-hydroxyl and 5'-monophosphoester termini which has been tentatively termed polyadenylase by others [7], also catalyzes the hydrolysis of single but not double-stranded RNA and DNA molecules [5,6] and is localized in the intermembrane space [7,12,13].