pol

DnaB

helicase

Core (a«>>)

Core (acu)

0 clamp (open)

FIGURE 5.12 DNA Polymerase lll—Assembly of Subunits

P clamp

P clamp (op«n)

(a)

FIGURĘ 25-10 DNA polymerase III. (a) Architccture of bactcrial DNA polymerase III. Two coce domains, composed of subunits a, a, and 0. arc linkcd by a fivc-subunit y complcx (also Icnown as thc clamp-loading complex) wilh the composilion r>yS6'. The y and r subunits arc cncodcd by thc same gcnc. The y subunit is a shortened yersion of r; the t subunit thus contains a domain identical to y, along with an additional segment that interacts with the core polymerase. The other two subunits of DNA polymerase III®, % and •)> (not shown), also bind to the y complex. Two 0 clamps interact with the two<ore subassembly, each clamp a dimer of the p subunit. The comple* in-trr.srts with ihc Dn.sB hchr.isc thmmeh rhp r suhimit fht Twn H suh-

A single core subunit is shown above and its assembly inlo a dimerk unit is shown below. The dimerk subunit contains onły one clamp loader, which is associafed with the logging strand synlhetic unit. The two core proteins are bound together by the tau subunit. The components of DNA polymerase III are the p subunits forming the sliding clamp, the epsilon and thela subunits and the clamp loader. When the DNA polymerase assembles, tau subunits join two nearfy identkal complexes together.

Cliu) maintains dimer

For

LKADINC

STRAND

SYNTHKSIS

For

LAGCING ST RAND SYNTHKSIS