4.7 Article

Interaction of the Escherichia coli HU Protein with Various Topological Forms of DNA

期刊

BIOMOLECULES
卷 11, 期 11, 页码 -

出版社

MDPI
DOI: 10.3390/biom11111724

关键词

HU; DNA supercoiling; affinity; chemical crosslinking

资金

  1. National Institutes of Health [GM-32253]
  2. U.S. Public Health Service
  3. National Natural Science Foundation of China [92051109, 91951000]

向作者/读者索取更多资源

E. coli histone-like protein HU shows a preference for binding to negatively supercoiled DNA, with affinity increasing with higher negative superhelical density. However, this binding preference becomes negligible at high HU/DNA mass ratios.
E. coli histone-like protein HU has been shown to interact with different topological forms of DNA. Using radiolabeled HU, we examine the effects of DNA supercoiling on HU-DNA interactions. We show that HU binds preferentially to negatively supercoiled DNA and that the affinity of HU for DNA increases with increases in the negative superhelical density of DNA. Binding of HU to DNA is most sensitively influenced by DNA supercoiling within a narrow but physiologically relevant range of superhelicity (sigma = -0.06-0). Under stoichiometric binding conditions, the affinity of HU for negatively supercoiled DNA (sigma = -0.06) is more than 10 times higher than that for relaxed DNA at physiologically relevant HU/DNA mass ratios (e.g., 1:10). This binding preference, however, becomes negligible at HU/DNA mass ratios higher than 1:2. At saturation, HU binds both negatively supercoiled and relaxed DNA with similar stoichiometries, i.e., 5-6 base pairs per HU dimer. In our chemical crosslinking studies, we demonstrate that HU molecules bound to negatively supercoiled DNA are more readily crosslinked than those bound to linear DNA. At in vivo HU/DNA ratios, HU appears to exist predominantly in a tetrameric form on negatively supercoiled DNA and in a dimeric form on linear DNA. Using a DNA ligase-mediated nick closure assay, we show that approximately 20 HU dimers are required to constrain one negative supercoil on relaxed DNA. Although fewer HU dimers may be needed to constrain one negative supercoil on negatively supercoiled DNA, our results and estimates of the cellular level of HU argue against a major role for HU in constraining supercoils in vivo. We discuss our data within the context of the dynamic distribution of the HU protein in cells, where temporal and local changes of DNA supercoiling are known to take place.

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