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Comparative Biochemical Properties of RNA-directed DNA Polymerases from Rauscher Murine Leukemia Virus and Avian Myeloblastosis Virus¹

Carcinogenesis Program, Biology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830

Various biochemical properties of the RNA-directed DNA polymerases of avian myeloblastosis virus and Rauscher murine leukemia virus were studied. Effects of divalent cations, pH, and temperature on the ability of the two polymerases to utilize various template primers are significantly different. The template primers tested include DNase-activated calf thymus DNA, d(A-T)_n, (rA)_n·(rU)_n, (rA)_n·(dT)_n, (rA)_n·(dT)₆, (dA)_n·(dT)₆, (rC)_n·(dG)₆, and (rI)_n·(dC)₆. All showed individual characteristic requirements of divalent cations, pH, and temperature for optimum activity with the two polymerases. A minor change in the optimal conditions usually resulted in a marked decrease in the detected polymerase activity. In kinetic experiments, initial deoxythymidine 5'-monophosphate incorporation appeared to be the rate-limiting step in the (rA)_n·(rU)_n-dependent activity of the murine virus polymerase, whereas this was less apparent with the avian virus polymerase. The d(A-T)_n-dependent activity of both purified virus polymerases is competitively inhibited by (rU)_n or (rG)_n.

¹ Research jointly sponsored by the Cancer Virus Program of the National Cancer Institute and the United States Atomic Energy Commission under contract with Union Carbide Corporation.

Received 3/27/74. Accepted 6/25/74.