Title: Model for the supercoiling reaction catalyzed by DNA gyrase
Abstract: Liu & Wang proposed that negative supercoiling of a covalently circular duplex DNA by DNA gyrase arises from successive cycles of coiling of the DNA around the enzyme molecule (Liu & Wang, 1978a). They thought that the uncoiling of the DNA segment wrapped around the enzyme occurs once it has been released from the enzyme and is mediated by the swivelase activity of DNA gyrase. In this paper, we elaborate another scheme for this uncoiling. We propose that both strands of the DNA duplex are cleaved inside the DNA segment coiled around the enzyme and that the two DNA ends so created are linked to a distinct gyrase subunit. Then uncoiling of the DNA segment bound to the enzyme is driven by a mechanical ATP dependent movement of these two subunits. When this movement is finished, both DNA ends are in front of each other again and the DNA circle can be closed. Based on this mechanism, a model which takes into account all the experimental data published to date is described for the complete supercoiling reaction. This model displays several distinctive features with respect to those previously proposed (Mizuuchi, O'Dea & Gellert, 1978a; Liu & Wang, 1978a); in particular one DNA gyrase molecule can achieve complete supercoiling without moving along DNA substrate, which makes the enzyme attach continuously to a specific DNA sequence during the supercoiling reaction. The existence of a unique DNA binding site on DNA gyrase also predicts that attachment of one enzyme molecule will not lead to the formation of loops in a circular DNA and consequently that the supercoil density will increase homogeneously in all parts of the DNA molecule during the supercoiling reaction. A possible role for DNA gyrase in the architecture of the prokaryotic chromosome is discussed in relation to our model.
Publication Year: 1980
Publication Date: 1980-01-01
Language: en
Type: article
Indexed In: ['crossref', 'pubmed']
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Cited By Count: 8
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