DNA polymerase III, clamp loader complex

GO:0043846 · Other · Multiprotein complex · Proposed

A heptamer that includes the tau and gamma products of the dnaX gene and the chi/psi subcomplex. Confers structural asymmetry that allows the polymerase to replicate both leading and lagging strands. [GO:0043846]

Synonyms: DNA polymerase III, DnaX complex; DNA polymerase III, DnaX subcomplex; clamp loader complex

Part of: DNA polymerase III complex (GO:0009360)

UniProt location names: UniProt Consortium, CC BY 4.0. Reference label and route sources.

Components

Component	Type	Part of / acts on	Grounding	Genes	Essential	Role
DNA polymerase III tau/gamma subunit	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	dnaX	UNKNOWN	AAA+ ATPase motor subunit class in the DNA polymerase III clamp-loader assembly. `GO:0043846` GO:0043846 defines the clamp-loader complex as including tau and gamma products of the dnaX gene. `PMID:12940977` McHenry 2003 describes the DnaX complex as an E. coli heptamer that includes tau and gamma products of the dnaX gene. `UniProtKB:P06710` UniProtKB P06710 is the reviewed E. coli K-12 dnaX entry for the DNA polymerase III tau/gamma subunit and is annotated to GO:0043846.
DNA polymerase III delta subunit	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	holA	UNKNOWN	Delta wrench subunit that binds the beta clamp during clamp-loader ring opening. `PMID:11525729` Jeruzalmi et al. 2001 solved an E. coli gamma complex structure with one delta subunit. `UniProtKB:P28630` UniProtKB P28630 is the reviewed E. coli K-12 holA entry for DNA polymerase III subunit delta and is annotated to GO:0043846.
DNA polymerase III delta' subunit	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	holB	UNKNOWN	Delta-prime stator subunit in the clamp-loader AAA+ assembly. `PMID:11525729` Jeruzalmi et al. 2001 solved an E. coli gamma complex structure with one delta-prime subunit. `UniProtKB:P28631` UniProtKB P28631 is the reviewed E. coli K-12 holB entry for DNA polymerase III subunit delta' and is annotated to GO:0043846.
DNA polymerase III chi subunit	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	holC	UNKNOWN	Chi subunit of the accessory chi/psi dimer in the DNA polymerase III clamp-loader complex. `GO:0043847` GO:0043847 defines the chi/psi subcomplex as a dimer composed of the chi and psi subunits. `UniProtKB:P28905` UniProtKB P28905 is the reviewed E. coli K-12 holC entry for DNA polymerase III subunit chi and is annotated to GO:0043846.
DNA polymerase III psi subunit	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	holD	UNKNOWN	Psi subunit of the accessory chi/psi dimer in the DNA polymerase III clamp-loader complex. `GO:0043847` GO:0043847 defines the chi/psi subcomplex as a dimer composed of the chi and psi subunits. `UniProtKB:P28632` UniProtKB P28632 is the reviewed E. coli K-12 holD entry for DNA polymerase III subunit psi and is annotated to GO:0043846.

Organism-specific protein examples

Named proteins in which each component's role was established, with the organism the evidence comes from. The component above is the taxon-agnostic family; these are the specific entries behind it.

DNA polymerase III tau/gamma subunit

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P06710`	DNA polymerase III subunit tau	dnaX	Escherichia coli K-12 (`NCBITaxon:83333`)	REVIEWED
Role and evidence (1 reference) Reviewed E. coli K-12 DnaX accession for the tau/gamma clamp-loader products. `UniProtKB:P06710` UniProtKB P06710 is the reviewed Escherichia coli K-12 dnaX entry for DNA polymerase III subunit tau.

DNA polymerase III delta subunit

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P28630`	DNA polymerase III subunit delta	holA	Escherichia coli K-12 (`NCBITaxon:83333`)	REVIEWED
Role and evidence (1 reference) Reviewed E. coli K-12 HolA accession for the clamp-loader delta subunit. `UniProtKB:P28630` UniProtKB P28630 is the reviewed Escherichia coli K-12 holA entry for DNA polymerase III subunit delta.

DNA polymerase III delta' subunit

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P28631`	DNA polymerase III subunit delta'	holB	Escherichia coli K-12 (`NCBITaxon:83333`)	REVIEWED
Role and evidence (1 reference) Reviewed E. coli K-12 HolB accession for the clamp-loader delta-prime subunit. `UniProtKB:P28631` UniProtKB P28631 is the reviewed Escherichia coli K-12 holB entry for DNA polymerase III subunit delta'.

DNA polymerase III chi subunit

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P28905`	DNA polymerase III subunit chi	holC	Escherichia coli K-12 (`NCBITaxon:83333`)	REVIEWED
Role and evidence (1 reference) Reviewed E. coli K-12 HolC accession for the clamp-loader chi subunit. `UniProtKB:P28905` UniProtKB P28905 is the reviewed Escherichia coli K-12 holC entry for DNA polymerase III subunit chi.

DNA polymerase III psi subunit

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P28632`	DNA polymerase III subunit psi	holD	Escherichia coli K-12 (`NCBITaxon:83333`)	REVIEWED
Role and evidence (1 reference) Reviewed E. coli K-12 HolD accession for the clamp-loader psi subunit. `UniProtKB:P28632` UniProtKB P28632 is the reviewed Escherichia coli K-12 holD entry for DNA polymerase III subunit psi.

Canonical examples

NCBITaxon:562 Escherichia coli — Source species for the solved gamma-complex structure. [PMID:11525729]

Functions

DNA clamp loader activity GO:0003689 — The DNA polymerase III clamp-loader complex opens the beta sliding-clamp ring and loads it around primer-template DNA using its ATPase motor.
- GO:0003689 GO:0003689 defines DNA clamp loader activity as ATP-hydrolysis-driven opening and closing of a sliding clamp around DNA duplex.
- PMID:11525729 Jeruzalmi et al. 2001 described the E. coli gamma complex as an AAA+ ATPase that loads the beta sliding clamp onto DNA.
DNA replication GO:0006260 — The clamp-loader complex helps the Pol III holoenzyme coordinate leading- and lagging-strand DNA replication.
- GO:0043846 GO:0043846 defines the clamp-loader complex by its structural asymmetry in leading- and lagging-strand replication.
- GO:0006260 GO:0006260 is the Gene Ontology biological-process term for DNA replication.

Mechanism graphs

Clamp loader assembles the beta clamp on DNA (FUNCTION)

The Pol III clamp loader combines DnaX, delta, delta-prime, chi, and psi subunits to open and load the beta sliding clamp on primer-template DNA.

Subject	Predicate	Object	Evidence
DNA polymerase III tau/gamma subunit	is part of	DNA polymerase III, clamp loader complex	`GO:0043846` GO:0043846 identifies the DnaX and chi/psi assemblies as parts of the clamp loader.
DNA polymerase III delta subunit	is part of	DNA polymerase III, clamp loader complex	`PMID:11525729` Jeruzalmi et al. 2001 solved an E. coli gamma complex structure with one delta subunit.
DNA polymerase III delta' subunit	is part of	DNA polymerase III, clamp loader complex	`PMID:11525729` Jeruzalmi et al. 2001 solved an E. coli gamma complex structure with one delta-prime subunit.
DNA polymerase III chi subunit	is part of	DNA polymerase III, clamp loader complex	`GO:0043847` GO:0043847 defines the clamp-loader chi/psi subcomplex as a dimer composed of chi and psi.
DNA polymerase III psi subunit	is part of	DNA polymerase III, clamp loader complex	`GO:0043847` GO:0043847 defines the clamp-loader chi/psi subcomplex as a dimer composed of chi and psi.
DNA polymerase III delta subunit	binds	DNA polymerase III, beta sliding clamp processivity factor complex	`PMID:11525729` Jeruzalmi et al. 2001 describe delta as free to bind beta in the open gamma-complex structure.
DNA polymerase III, clamp loader complex	loads	DNA polymerase III, beta sliding clamp processivity factor complex	`GO:0003689` GO:0003689 defines DNA clamp-loader activity as opening and closing a sliding clamp around DNA. `PMID:11525729` Jeruzalmi et al. 2001 describe the gamma complex as loading the beta sliding clamp onto DNA.
DNA polymerase III, clamp loader complex	acts on	primer-template DNA	`GO:0009360` GO:0009360 states that the clamp-loading complex assembles the beta processivity factor onto the primer template.
DNA polymerase III, clamp loader complex	supports	DNA replication	`GO:0043846` GO:0043846 defines the complex by its contribution to structural asymmetry for leading- and lagging-strand replication.

Discussions

CURATION_TODO (OPEN): Resolve exact source-neutral DnaX, HolA, HolB, HolC, and HolD family grounding for DNA polymerase III clamp-loader components. This first GO:0043846 split captures reviewed E. coli K-12 UniProtKB examples for the clamp-loader subunits while leaving source-neutral protein-family grounding to a later InterPro/Pfam/NCBIfam review.

Evidence

GO:0043846 Gene Ontology cellular-component term for the DNA polymerase III clamp-loader complex.
GO:0043847 Gene Ontology cellular-component term for the chi/psi subcomplex that contributes two clamp-loader subunits.
GO:0032991 Gene Ontology cellular-component parent term for protein-containing complexes.
GO:0009360 Gene Ontology cellular-component term for the DNA polymerase III holoenzyme that contains the clamp loader.
GO:0003689 Gene Ontology molecular-function term for DNA clamp loader activity.
GO:0006260 Gene Ontology biological-process term for DNA replication.
PMID:11525729 PubMed identifier for Jeruzalmi, O'Donnell and Kuriyan 2001, Crystal structure of the processivity clamp loader gamma complex of E. coli DNA polymerase III.
DOI:10.1016/s0092-8674(01)00463-9 DOI for Jeruzalmi et al. 2001 as reported by PubMed.
PMID:12940977 PubMed identifier for McHenry 2003, Chromosomal replicases as asymmetric dimers: studies of subunit arrangement and functional consequences.
DOI:10.1046/j.1365-2958.2003.03645.x DOI for McHenry 2003 as reported by PubMed.
UniProtKB:P06710 Reviewed UniProtKB accession for E. coli K-12 DnaX.
UniProtKB:P28630 Reviewed UniProtKB accession for E. coli K-12 HolA.
UniProtKB:P28631 Reviewed UniProtKB accession for E. coli K-12 HolB.
UniProtKB:P28905 Reviewed UniProtKB accession for E. coli K-12 HolC.
UniProtKB:P28632 Reviewed UniProtKB accession for E. coli K-12 HolD.

Curation history

2026-09-28T10:48:48Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-28T10:50:12Z codex · EXPANDED_RECORD — Added GO synonyms, protein-containing-complex parentage, Pol III holoenzyme parthood, five reviewed E. coli K-12 protein examples, clamp-loading and DNA-replication functions, GO/PubMed/UniProtKB evidence, a nonmechanistic clamp-loading graph, and a grounding TODO.
2026-09-28T10:51:00Z codex · REFINED_EVIDENCE — Replaced GO-only delta and delta-prime graph edge evidence with the E. coli gamma-complex structure paper.
2026-09-28T11:05:33Z codex · FIX_REVIEW_ISSUES — Fixed #1718 by scoping chi/psi graph evidence to GO:0043847 and fixed #1719 by narrowing the canonical E. coli example note.
2026-09-28T11:20:20Z codex · FIX_REVIEW_ISSUE — Fixed #1720 by removing the shared YAML alias from chi/psi evidence.

Source: data/structures/other/dna_polymerase_iii_clamp_loader_complex.yaml