Two DNA polymerases purified from normal human lymphocytes are distinguishable from the viral reverse transcriptases of avian myeloblastosis virus and Mason-Pfizer monkey virus by their relative affinity for select templates. In this respect, the activity of the two normal human lymphocyte polymerases closely resembles the activity of Escherichia coli DNA polymerase 1. The viral and cellular DNA polymerases are equally active with the nonspecific template, poly(rA) . poly(dT). Criteria for distinguishing the activity of viral reverse transcriptase are discussed.

The DNA polymerase from the Mason-Pfizer monkey virus (M-PMV), an RNA tumor virus not typical type-C or type-B, has been purified a thousand-fold over the original crude viral suspension. This purified enzyme is compared to a similarly purified DNA polymerase from the primate woolly monkey virus, a type-C virus. The two enzymes have similar template specificities but differ in their requirements for optimum activity. Both DNA polymerases have a pH optimum of 7.3 in Tris buffer. M-PMV enzyme has maximum activity with 5 mM Mg2+ and 40 mM potassium chloride, whereas the woolly monkey virus optima are 100 mM potassium chloride with 0.8 mM Mn2+. The apparent molecular weight of the M-PMV enzyme is approximately 110,000, whereas the woolly monkey virus polymerase is approximately 70,000. The biochemical properties of these two enzymes were also compared to a similarly purified enzyme from a type-C virus from a lower mammal (Rauscher murine leukemia virus). The results show that more similarity exists between the DNA polymerases from viruses of the same type (type-C), than between the polymerases from viruses of different types but from closely related species.

DNA polymerase III is an enzyme activity in eukaryotic cells which under certain conditions shows strong preference for polyadenylic acid as template when primed by oligodeoxythymidylate. Its first complete separation from other DNA polymerases in human lymphoblasts is reported. This enzyme is biochemically and immunologically distinct from DNA polymerase I and from viral reverse transcriptase from a primtate type C virus.

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