single-stranded DNA-binding protein complex

GO:0044777 · Other · Multiprotein complex · Proposed

A homotetrameric single-stranded DNA-binding protein assembly that binds and stabilizes single-stranded DNA during DNA replication, recombination, and repair. [GO:0044777]

Synonyms: SSB complex

Part of: nucleoid (GO:0009295)

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

Components

Component	Type	Part of / acts on	Grounding	Genes	Stoichiometry	Essential	Role
single-stranded DNA-binding protein	Protein	part of	`InterPro:IPR011344`	ssb	4 copies per homotetrameric SSB complex		SSB subunit family that forms the homotetrameric single-stranded DNA-binding complex. `GO:0044777` GO:0044777 defines the single-stranded DNA-binding protein complex as homotetrameric. `InterPro:IPR011344` InterPro IPR011344 is a family entry named Single-stranded DNA-binding protein and is annotated to GO:0003697 and GO:0006260. `PDB:1KAW` RCSB PDB:1KAW assembly 1 is an author-defined E. coli SSB homo-4-mer, and polymer entity 1 contains four SSB chains.

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.

single-stranded DNA-binding protein

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P0AGE0`	Single-stranded DNA-binding protein	ssb	Escherichia coli K-12 (`NCBITaxon:83333`)	REVIEWED
Role and evidence (2 references) Reviewed E. coli K-12 SSB accession mapped by RCSB to the four protein chains in PDB:1KAW. `UniProtKB:P0AGE0` UniProtKB P0AGE0 is the reviewed Escherichia coli K-12 SSB entry for gene ssb. `PDB:1KAW` RCSB maps PDB:1KAW polymer entity 1 to UniProtKB:P0AGE0.

Canonical examples

NCBITaxon:562 Escherichia coli — Bacterial source of the SSB DNA-binding-domain tetramer crystallized as PDB:1KAW and of the SSB-DNA crystal structure deposited as PDB:1EYG. [PDB:1KAW]

Functions

single-stranded DNA binding GO:0003697 — The SSB complex binds exposed single-stranded DNA, including ssDNA generated during DNA replication.
- GO:0003697 GO:0003697 is the molecular-function term for binding to single-stranded DNA.
- PDB:1EYG PDB:1EYG contains E. coli SSB DNA-binding-domain chains with 35-mer single-stranded DNA polymers.

Mechanism graphs

SSB binds single-stranded DNA (FUNCTION)

The homotetrameric SSB complex uses its SSB protein subunits to form a DNA-binding complex that binds single-stranded DNA.

Subject	Predicate	Object	Evidence
single-stranded DNA-binding protein	contributes to	single-stranded DNA binding	`GO:0044777` GO:0044777 defines the SSB complex as a homotetrameric single-stranded DNA-binding protein complex. `InterPro:IPR011344` InterPro IPR011344 is a single-stranded DNA-binding protein family annotated to GO:0003697. `PDB:1KAW` PDB:1KAW assembly 1 is an author-defined homo-4-mer with four copies of polymer entity 1.
single-stranded DNA-binding protein complex	binds	single-stranded DNA	`GO:0003697` GO:0003697 defines single-stranded DNA binding as binding to single-stranded DNA. `PDB:1EYG` PDB:1EYG resolves E. coli SSB DNA-binding-domain chains bound to single-stranded DNA polymers.
single-stranded DNA-binding protein complex	enables	single-stranded DNA binding	`GO:0044777` GO:0044777 defines the SSB complex by its single-stranded DNA-binding activity. `GO:0003697` GO:0003697 is the molecular-function term for single-stranded DNA binding.

Evidence

GO:0044777 Gene Ontology cellular-component term for the single-stranded DNA-binding protein complex.
GO:0032991 Gene Ontology cellular-component term for protein-containing complexes.
GO:0009295 Gene Ontology cellular-component term for the nucleoid; GO:0044777 is part_of this term.
GO:0003697 Gene Ontology molecular-function term for single-stranded DNA binding.
GO:0006260 Gene Ontology biological-process term for DNA replication.
InterPro:IPR011344 InterPro family for single-stranded DNA-binding proteins.
UniProtKB:P0AGE0 UniProtKB reviewed Escherichia coli K-12 SSB entry.
DOI:10.1073/pnas.94.13.6652 Raghunathan et al. 1997, Crystal structure of the homo-tetrameric DNA binding domain of Escherichia coli single-stranded DNA-binding protein, PNAS.
PMID:9192620 PubMed identifier for Raghunathan et al. 1997 as reported by RCSB PDB:1KAW.
DOI:10.1038/77943 Raghunathan et al. 2000, Structure of the DNA binding domain of E. coli SSB bound to ssDNA, Nature Structural Biology.
PMID:10932248 PubMed identifier for Raghunathan et al. 2000 as reported by RCSB PDB:1EYG.
PDB:1KAW RCSB Protein Data Bank entry for the E. coli SSB DNA-binding-domain homo-4-mer from Raghunathan et al. 1997.
PDB:1EYG RCSB Protein Data Bank entry for E. coli SSB DNA-binding-domain chains bound to single-stranded DNA from Raghunathan et al. 2000.

Curation history

2026-09-24T10:00:36Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-24T10:01:32Z codex · EXPANDED_RECORD — Added SSB synonymy, protein-complex parentage and nucleoid parthood, an InterPro-grounded SSB component with UniProt and PDB evidence, an Escherichia coli canonical example, single-stranded-DNA-binding function evidence, and a compact function graph.
2026-09-24T10:12:22Z codex · ADDRESS_REVIEW — #1477: replaced a dynamic SSB oligomerization graph edge with a static component-contribution claim supported by GO:0044777, InterPro:IPR011344, and PDB:1KAW.
2026-09-24T10:13:01Z codex · TIGHTEN_REVIEW_WORDING — #1477: tightened SSB component prose to avoid phrasing the tetrameric stoichiometry evidence as a dynamic oligomerization claim.
2026-09-24T10:13:38Z codex · TIGHTEN_REVIEW_WORDING — #1477: tightened the SSB graph scope note to describe tetrameric composition rather than tetramerization.

Source: data/structures/other/single_stranded_dna_binding_protein_complex.yaml