ISOLATION AND PROPERTIES OF A NUCLEIC ACID HYBRID POLYMERASE

Synthetic RNA-dependent DNA polymerase activity in normal rat liver and hepatomas

Normal adult rat liver contains a high level of a synthetic RNA-dependent DNA polymerase activity, which is distinct from cellular DNA-dependent polymerases. It uses poly(dT).poly(rA) and poly(rA).poly(rU) as templates but has little or no response to DNA or several single-stranded RNAs.

Distinguishing reverse transcriptase of an RNA tumor virus from other known DNA polymerases

Assays are described that permit one to distinguish the reverse transcriptase of RNA tumor viruses from known normal cellular DNA-instructed DNA polymerases. Template responses of purified reverse transcriptase were compared with those of similar preparations of the DNA polymerase I of Escherichia coli and of calf-thymus polymerase. All three enzymes responded well to the synthetic duplexes poly(dT).poly(A), poly(U).poly(A), and poly(dT).poly(dA). Hence, these duplexes can detect, but cannot distinguish reverse, transcriptase from the known normal DNA polymerases. However, certain oligomer-homopolymer complexes serve as excellent distinguishing agents. The reverse transcriptase responds very well to (dT)(10).poly(A) and very poorly to (dT)(10).poly(dA), whereas both cellular DNA polymerases do not exhibit this behavior.Purified single-stranded RNA also serves as a diagnostic device, since only reverse transcriptase gives a detectable response. To be definitive, a positive response to RNA must be accompanied by a demonstration via molecular hybridization that the DNA product is complementary to the RNA and not to some minor DNA contaminant.

Nucleic acid polymerases of the developing chicken embryo: a DNA polymerase preferring a hybrid template

This paper presents a preliminary survey of the nucleic acid polymerases of the developing chicken embryo, especially of the 4-day stage. The predominant activity is that of a DNA polymerase preferring a DNA-RNA hybrid as the template. The enzyme, which is activated by Mn(2+) ions and inhibited by p-chloromercuriphenylsulfonate, copies preferentially the ribo strand of a hybrid, such as poly(rA).poly(dT), but is relatively inactive with all-ribo duplexes. DNA polymerase I of Escherichia coli was also found to use the hybrid template with high efficiency, copying preferentially the ribo strand. With the chicken enzyme, the template activity of denatured DNA was increased tenfold by simultaneous transcription with RNA polymerase. DNA polymerase activity reaches a maximum in the 6- to 8-day chicken embryo and then declines progressively to about one-third of the maximal value in the adult chicken.