Replication clamp complexes

Two other protein complexes also function in eukaryotic DNA replication. RPA (replication protein A) is a eukaryotic single-stranded DNA-binding protein, equivalent in function to the E. coli SSB protein. RFC (replication/actor (J) is a clamp loader for PCNA and facilitates the assembly of active replication complexes. The subunits of the RFC complex have significant sequence similarity to the subunits of the bacterial clamploading (y) complex. 

High-fidelity chromosomal replication in E. coli is executed by a multicomponent complex referred to as DNA polymerase III holoenzyme (see Fig. 4a) (18-21). Pol 111 holoenzyme consists of three main subcomponents Pol 111 core, 3-clamp, and y-complex clamp-loader. Pol 111 core is the replicative DNA polymerase that consists of three subunits (a, e, 0) a exhibits DNA polymerase activity, e performs 3 -5 exonuclease activity necessary for proofreading, and the function of 0 is currently unclear. 

Bermudez VP, Lindsey-Boltz LA, Cesare AJ, Maniwa Y, Griffith JD, Hurwitz J, Sancar A. Loading of the human 9-1-1 checkpoint complex onto DNA by the checkpoint clamp loader hRadl7-replication factor C complex in vitro. Proc. Natl. Acad. Sci. U.S.A. 2003 100(4) 1633-1638. 

The polymerase holoenzyme assembles. The DNA polymerase ITT holoen-zyme assembles on the prepriming complex, initiated by interactions between DnaB and the sliding clamp subunit of DNA polymerase 111. These interactions also trigger ATP hydrolysis within the DnaA subunits, signaling the initiation of DNA replication. The breakup of the DnaA assembly prevents additional rounds of replication from beginning at the replication origin. 

Family C of DNA polymerases is presented exceptionally by bacterial enzymes involved in replicative processes. So, the DNA polymerase III holoenzyme is the main enzyme realizing the DNA replication in Escherichia coli. Bacillus subtilis, and belongs to family C polymerases. It consists of three assemblies the pol 111 core, the beta sliding clamp processivity factor and the clamp-loading complex. The core consists of three subunits—a, the polymerase activity hub, 8, exonucleolytic proofreader, and 0, which may act as a stabilizer for e. The holoenzyme contains two cores, one for each strand, the lagging and leading [19]. The beta shding clamp processivity factor is also present in duplicate, one for each core, to create a clamp... 

Supramolecular structures such as rotaxanes occasionally play important roles in enzymatic activities. For example, DNA polymerases contain sliding clamps in which the ring-shaped protein assemblies form supramolecular complexes. The ring-shaped clamp peptides of DNA (or RNA) polymerases participate in binding two polynucleotide chains for replication. ° The clamps have no active sites and replication of polynucleotides is difficult without clamps. Similarly, cyclodextrins (CDs) and other host molecules are ring-shaped host molecules that include various guests to form supramolecular complexes such as rotaxanes. ... 

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