Properties of a ribonucleic acid synthesizing system in cell-free extracts of tobacco leaves

The capacity of tobacco-leaf extracts to incorporate ATP and GTP into a cold-trichloroacetic-acid insoluble product has been studied. Almost all the four nucleotide-dependent incorporating activity is localized in the 1000 × g fraction of such extracts. The RNA character of the product is indicated by the dependence of the reaction on all four nucleotides (ATP, GTP, UTP, and CTP), by the fact that the product is readily solubilized by RNAase treatment, and the fact that both ATP and GTP are incorporated at comparable rates. The incorporation of [³²P]ATP is enhanced by the addition of an ATP-generating system. The system is inhibited by the presence of DNAase, RNAase, or actinomycin D in the incubation mixtures. The product of incorporation is solubilized by RNAase but not by DNAase. Pretreatment of the 1000 × g fraction with DNAase or actinomycin D destroys the RNA synthesizing capacity. Within the 1000 × g fraction, RNA synthesizing activity was associated with both chloroplasts and nuclei, the former being the major site of activity.