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Origin-Specific Unwinding of Herpes Simplex Virus 1 DNA by the Viral UL9 and ICP8 Proteins: Visualization of a Specific Preunwinding Complex
Alexander M. Makhov, Sam S. -K. Lee, I. Robert Lehman and Jack D. Griffith
Proceedings of the National Academy of Sciences of the United States of America
Vol. 100, No. 3 (Feb. 4, 2003), pp. 898-903
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/3138257
Page Count: 6
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Herpes simplex virus 1 contains three origins of replication; two copies of oriS and one of a similar sequence, oriL. Here, the combined action of multiple factors known or thought to influence the opening of oriS are examined. These include the viral origin-binding protein, UL9, and single-strand binding protein ICP8, host cell topoisomerase I, and superhelicity of the DNA template. By using electron microscopy, it was observed that when ICP8 and UL9 proteins were added together to oriS-containing supertwisted DNA, a discrete preunwinding complex was formed at oriS on 40% of the molecules, which was shown by double immunolabeling electron microscopy to contain both proteins. This complex was relatively stable to extreme dilution. Addition of ATP led to the efficient unwinding of ≈50% of the DNA templates. Unwinding proceeded until the acquisition of a high level of positive supertwists in the remaining duplex DNA inhibited further unwinding. Addition of topoisomerase I allowed further unwinding, opening >1 kb of DNA around oriS.
Proceedings of the National Academy of Sciences of the United States of America © 2003 National Academy of Sciences