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DNA endonucleases associated with the avian myeloblastosis virus DNA polymerase
Abstract:
A DNA endonuclease, Endo-I, which cleaves superhelical DNAs, has been isolated from avian myeloblastosis virions stripped of their coats by mild detergent treatment. The enzyme has a broad pH optimum around 7.5-8.0 and requires Mg2+ for activity. A second endonuclease, Endo-II, with a requirement for Mn2+, also present in viral cores, copurified with avian myeloblastosis virus alpha beta DNA polymerase (reverse transcriptase, RNA-dependent DNA nucleotidyltransferase) and similarly cleaved superhelical DNAs. Heat denaturation and sodium fluoride and N-ethylmaleimide inhibition studies were carried out to demonstrate a possible relationship between the two endonucleases and the viral DNA polymerase and RNase H activities. It appears that Endo-II may be an intrinsic activity of the polymerase.
Insights
Researchers isolated two DNA endonucleases, Endo-I and Endo-II, from avian myeloblastosis virus. Endo-II, requiring manganese, appears to be an intrinsic activity of the viral DNA polymerase.
Area of Science:
- Virology
- Molecular Biology
- Enzymology
Background:
- Avian myeloblastosis virus (AMV) contains enzymes essential for its replication.
- Understanding viral enzymes aids in comprehending viral life cycles and developing antiviral strategies.
Purpose of the Study:
- To isolate and characterize DNA endonucleases from AMV.
- To investigate the relationship between these endonucleases and viral polymerase activities.
Main Methods:
- Isolation of endonucleases from detergent-stripped AMV virions.
- Biochemical characterization of enzyme activity, including pH optima and cofactor requirements (Mg2+, Mn2+).
- Enzyme inhibition studies (heat denaturation, N-ethylmaleimide, sodium fluoride) to assess relationships with viral polymerase and RNase H.
Main Results:
- Two DNA endonucleases, Endo-I and Endo-II, were isolated.
- Endo-I cleaved superhelical DNA and required Mg2+.
- Endo-II cleaved superhelical DNA, required Mn2+, copurified with AMV DNA polymerase, and exhibited characteristics suggesting it is an intrinsic polymerase activity.
Conclusions:
- AMV virions contain at least two distinct DNA endonuclease activities.
- Endo-II likely represents an intrinsic nuclease activity of the AMV alpha beta DNA polymerase (reverse transcriptase).
- These findings contribute to the understanding of the enzymatic machinery of retroviruses.