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The Bacillus subtilis primosomal protein DnaD untwists supercoiled DNA

Zhang, Wenke; Allen, Stephanie; Roberts, Clive J.; Soultanas, Panos


Wenke Zhang

Professor of Pharmaceutical Biophysics

Clive J. Roberts


The essential Bacillus subtilis DnaD and DnaB proteins have been implicated in the initiation of DNA replication. Recently, DNA remodeling activities associated with both proteins were discovered that could provide a link between global or local nucleoid remodeling and initiation of replication. DnaD forms scaffolds and opens up supercoiled plasmids without nicking to form open circular complexes, while DnaB acts as a lateral compaction protein. Here we show that DnaD-mediated opening of supercoiled plasmids is accompanied by significant untwisting of DNA. The net result is the conversion of writhe (Wr) into negative twist (Tw), thus maintaining the linking number (Lk) constant. These changes in supercoiling will reduce the considerable energy required to open up closed circular plectonemic DNA and may be significant in the priming of DNA replication. By comparison, DnaB does not affect significantly the supercoiling of plasmids. Binding of the DnaD C-terminal domain (Cd) to DNA is not sufficient to convert Wr into negative Tw, implying that the formation of scaffolds is essential for duplex untwisting. Overall, our data suggest that the topological effects of the two proteins on supercoiled DNA are different; DnaD opens up, untwists and converts plectonemic DNA to a more paranemic form, whereas DnaB does not affect supercoiling significantly and condenses DNA only via its lateral compaction activity. The significance of these findings in the initiation of DNA replication is discussed.


Zhang, W., Allen, S., Roberts, C. J., & Soultanas, P. (2006). The Bacillus subtilis primosomal protein DnaD untwists supercoiled DNA. Journal of Bacteriology, 188(15),

Journal Article Type Article
Publication Date Aug 1, 2006
Deposit Date Aug 12, 2009
Publicly Available Date Aug 12, 2009
Journal Journal of Bacteriology
Print ISSN 0021-9193
Electronic ISSN 0021-9193
Publisher American Society for Microbiology
Peer Reviewed Peer Reviewed
Volume 188
Issue 15
Public URL
Publisher URL


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