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The E.coli DnaB helicase is essential for replication initiation from the chromosomal origin of replication ( oriC ) and is present in vivo as a protein complex with six monomers of the DnaC ATPase protein and six ATP molecules (Wickner and Hurwitz, 1975; Lanka and Schuster, 1983). DNA replication initiation at oriC begins with binding of multiple molecules of the bacterial DnaA initiator protein to a 9 bp repeats (DnaA boxes). This binding promotes destabilization of nearby AT-rich sequences, resulting in unwinding of the DNA double helix and the formation of an open complex.

I looked up in DNA Replication by Arthur Kornberg, Tania A. Baker (the authors who probably coined this term), Google and Google.Scholar but didn't stumble upon any definition.

What is it actually?

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The sentence itself is actually the definition of open complex: It is the structure that is created once the DNA double helix is unwinded due to the DnaA proteins.

This binding promotes destabilization of nearby AT-rich sequences, resulting in unwinding of the DNA double helix and the formation of an open complex.

I have also found a papera co-authored by Arthur Kornberg himself where the authors self-define "open complex" as well:

Three tandem repeats of a 13-mer in the AT-rich region are essential to the unique replication origin of E. coli and of remotely related Enterobacteriaceae. These iterated sequences are identified by deletion analysis and sensitivities to endonucleases as the site for initial duplex opening by the initiator dnaA protein. This “open complex” requires ATP and 38% for optimum formation and stability.

There are several papersb,c that use "open complex" in the same way.

References:

a David Bramhill, Arthur Kornberg, Duplex opening by dnaA protein at novel sequences in initiation of replication at the origin of the E. coli chromosome, Cell, Volume 52, Issue 5, 1988, Pages 743-755, ISSN 0092-8674, http://dx.doi.org/10.1016/0092-8674(88)90412-6. (http://www.sciencedirect.com/science/article/pii/0092867488904126)

b Ozaki, Shogo, et al. "A common mechanism for the ATP-DnaA-dependent formation of open complexes at the replication origin." Journal of Biological Chemistry 283.13 (2008): 8351-8362. (http://www.jbc.org/content/283/13/8351.full)

c Mukhopadhyay, Gauranga, et al. "Open-complex formation by the host initiator, DnaA, at the origin of P1 plasmid replication." The EMBO journal 12.12 (1993): 4547. (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC413885/)

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  • $\begingroup$ Thank you. Hope you don't mind if I take some time to respond to your entry. $\endgroup$ – Tyto alba May 17 '17 at 12:35
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An open complex is the complex of RNA polymerase and one DNA strand (antisense strand). Whereas closed strand means that RNA ploymerase is attached to both strands of the DNA.

Procedure: RNA Polymerase first creates the closed compex.

Then open complex is created when the double stranded DNA is separated to two strands.

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  • $\begingroup$ I saw this term used in transcription too. But I'm interested in replication solely. $\endgroup$ – Tyto alba Dec 17 '16 at 17:33

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