DnaX Complex Composition and Assembly Within Cells
DnaX is the ATPase that drives assembly of β2 onto DNA in concert with the δ, δ’, χ, and ψ subunits of the DnaX complex. The dnaX gene in E. coli expresses two proteins τ and γ by a programmed translational frameshifting mechanism. Although proposals have been made that the γ subunit might have functions distinct from the replicase, the abundance of evidence points to a DnaXcx that contains two copies of τ and one of γ. τ performs special roles that γ cannot, because it lacks domains that interact with the DnaB helicase and Pol III α. τ is essential for dimerizing the replicase, holding the leading and lagging strand together and tethering the DNA polymerase III holoenzyme to the DnaB helicase, serving as the central organizer of the replisome. It is also essential to allow rapid chaperoning of Pol III onto β2after its assembly onto DNA. This raises questions regarding the role of γ. A proposal has been made that its function is to avoid a third polymerase in the replisome...
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