Deoxyribonucleic acid-dependent incorporation of nucleotides from nucleoside triphosphates into ribonucleic acid.

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After the discovery of polynucleotide phosphorylasel a search was started in several laboratories for other enzymes which might be concerned with RNA2 synthesis. The main reason for this was that, contrary to DNA polymerase,3 polynucleotide phosphorylase did not appear to provide a mechanism for nucleic acid replication. Furthermore, since RNA is supposedly the carrier of genetic information from DNA to protein, a system for RNA replication might be expected to require DNA for activity. As a result of this search animal and bacterial cells (rat liver nuclei,4 Micrococcus lysodeikticus,5 Escherichia coli'6 7) were found to contain enzymes which bring about a DNA-dependent incorporation of nucleotides froln ribonucleoside triphosphates into RNA. The need for DNA and the fact that all four triphosphates (ATP, GTP, UTP, CTP) were required for maximal incorporation suggested a replication mechanism. However, while participation of polynucleotide phosphorylase in the observed incorporations was unlikely, it was not rigorously excluded, nor was the possibility ruled out that DNA might act indirectly by inhibiting nucleases present in the enzyme preparations. This paper reports on preliminary studies with enzyme preparations from two microorganisms, Lactobacillus arabinosus and Azotobacter vinelandii which, in agreement with the above observations, were found to catalyze a DNA-dependent incorporation of labeled ATP or GTP into RNA from mixtures of ATP, GTP, UTP, and CTP. Participation of polynucleotide phosphorylase was ruled out by (a) absence of this enzyme from L. arabinosus extracts, confirming earlier observations,' and (b) inorganic phosphate inhibition of its RNA-synthesizing activity in .4. vinelandii preparations without affecting nucleotide incorporation from nucleoside triphosphates. Indications were also obtained that DNA is directly involved in the latter reaction.