Summary: DNA polymerase III beta subunit, central domain

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Wikipedia: DNA clamp
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DNA clamp Edit Wikipedia article

Top and side views of a homotrimer of the human PCNA sliding clamp (rainbow colored, N-terminus = blue, C-terminus = red) with double stranded DNA modeled through the central pore (magenta).^[1]

A DNA clamp, also known as a sliding clamp, is a protein fold that serves as a processivity-promoting factor in DNA replication. As a critical component of the DNA polymerase III holoenzyme, the clamp protein binds DNA polymerase and prevents this enzyme from dissociating from the template DNA strand. The clamp-polymerase protein–protein interactions are stronger and more specific than the direct interactions between the polymerase and the template DNA strand; because one of the rate-limiting steps in the DNA synthesis reaction is the association of the polymerase with the DNA template, the presence of the sliding clamp dramatically increases the number of nucleotides that the polymerase can add to the growing strand per association event. The presence of the DNA clamp can increase the rate of DNA synthesis up to 1,000-fold compared with a nonprocessive polymerase.^[2]

Structure

The DNA clamp fold is an α+β protein that assembles into a multimeric structure that completely encircles the DNA double helix as the polymerase adds nucleotides to the growing strand.^[3] The DNA clamp assembles on the DNA at the replication fork and "slides" along the DNA with the advancing polymerase, aided by a layer of water molecules in the central pore of the clamp between the DNA and the protein surface. Because of the toroidal shape of the assembled multimer, the clamp cannot dissociate from the template strand without also dissociating into monomers.

The DNA clamp fold is found in bacteria, archaea, eukaryotes and some viruses. In bacteria, the sliding clamp is a homodimer composed of two identical beta subunits of DNA polymerase III and hence is referred to as the beta clamp. In archaea^[4] and eukaryotes, it is a trimer composed of three molecules of PCNA. The T4 bacteriophage also uses a sliding clamp, called gp45 that is a trimer similar in structure to PCNA but lacks sequence homology to either PCNA or the bacterial beta clamp.^[3]

Kingdom	Sliding clamp protein	Aggregation state	Associated polymerase
Bacteria	beta subunit of pol III	dimer	DNA polymerase III
Archaea	archaeal PCNA	trimer	pol ε
Eukaryote	PCNA	trimer	DNA polymerase delta
Virus	gp43 / gp45	trimer	RB69 Pol / T4 Pol

Bacterial

DNA polymerase III subunit beta

Crystallographic structure of the dimeric DNA polymerase beta subunit from E. coli.^[5]
Identifiers
Organism	Escherichia coli
Symbol	dnaN
Entrez	948218
PDB	1MMI
RefSeq (Prot)	NP_418156
UniProt	P0A988
Other data
EC number	2.7.7.7
Chromosome	MG1655: 3.88 - 3.88 Mb

The beta clamp is a specific DNA clamp and a subunit of the DNA polymerase III holoenzyme found in bacteria. Two beta subunits are assembled around the DNA by the gamma subunit and ATP hydrolysis; this assembly is called the pre-initiation complex. After assembly around the DNA, the beta subunits' affinity for the gamma subunit is replaced by an affinity for the alpha and epsilon subunits, which together create the complete holoenzyme.^[6]^[7]^[8] DNA polymerase III is the primary enzyme complex involved in prokaryotic DNA replication.

The gamma complex of DNA polymerase III, composed of γδδ'χψ subunits, catalyzes ATP to chaperone two beta subunits to bind to DNA. Once bound to DNA, the beta subunits can freely slide along double stranded DNA. The beta subunits in turn bind the αε polymerase complex. The α subunit possesses DNA polymerase activity and the ε subunit is a 3’-5’ exonuclease.^[8]

The beta chain of bacterial DNA polymerase III is composed of three topologically equivalent domains (N-terminal, central, and C-terminal). Two beta chain molecules are tightly associated to form a closed ring encircling duplex DNA.

DNA polymerase III, beta chain

Identifiers

Symbol

DNA_polIII_beta

Available protein structures:
Pfam	structures
PDB	RCSB PDB; PDBe; PDBj
PDBsum	structure summary

DNA polymerase III, beta chain,
N-terminal

Identifiers

Symbol

DNA_pol3_beta

Available protein structures:
Pfam	structures
PDB	RCSB PDB; PDBe; PDBj
PDBsum	structure summary

DNA polymerase III, beta chain,
central

Identifiers

Symbol

DNA_pol3_beta_2

Available protein structures:
Pfam	structures
PDB	RCSB PDB; PDBe; PDBj
PDBsum	structure summary

DNA polymerase III, beta chain,
C-terminal

Identifiers

Symbol

DNA_pol3_beta_3

Available protein structures:
Pfam	structures
PDB	RCSB PDB; PDBe; PDBj
PDBsum	structure summary

As a drug target

Certain NSAIDs (carprofen, bromfenac, and vedaprofen) exhibit some suppression of bacterial DNA replication by inhibiting bacterial DNA clamp.^[9]

Eukaryote

proliferating cell nuclear antigen
The assembled human DNA clamp, a trimer of the human protein PCNA.^[10]
Identifiers
Symbol	PCNA
Entrez	5111
HUGO	8729
OMIM	176740
PDB	1axc (RCSB PDB PDBe PDBj)
RefSeq	NM_002592
UniProt	P12004
Other data
Locus	Chr. 20 pter-p12

The sliding clamp in eukaryotes is assembled from a specific subunit of DNA polymerase delta called the proliferating cell nuclear antigen (PCNA). The N-terminal and C-terminal domains of PCNA are topologically identical. Three PCNA molecules are tightly associated to form a closed ring encircling duplex DNA.

The sequence of PCNA is well conserved between plants and animals, indicating a strong selective pressure for structure conservation, and suggesting that this type of DNA replication mechanism is conserved throughout eukaryotes.^[11] Homologues of PCNA have also been identified in the archaea (Euryarchaeota and Crenarchaeota) and in Paramecium bursaria Chlorella virus 1 (PBCV-1) and in nuclear polyhedrosis viruses.

Proliferating cell nuclear antigen, N-terminal domain

Identifiers

Symbol

PCNA_N

Available protein structures:
Pfam	structures
PDB	RCSB PDB; PDBe; PDBj
PDBsum	structure summary

Proliferating cell nuclear antigen, C-terminal domain

Identifiers

Symbol

PCNA_C

Available protein structures:
Pfam	structures
PDB	RCSB PDB; PDBe; PDBj
PDBsum	structure summary

Viral

DNA polymerase accessory protein 45

Crystallographic structure of the trimeric gp45 sliding clamp from bacteriophage T4.^[12]
Identifiers
Organism	Enterobacteria phage T4
Symbol	gp45
Entrez	1258821
PDB	1CZD
RefSeq (Prot)	NP_049666
UniProt	P04525
Other data
EC number	2.7.7.7
Chromosome	1: 0.03 - 0.03 Mb

The viral gp45 sliding clamp subunit protein contains two domains. Each domain consists of two alpha helices and two beta sheets – the fold is duplicated and has internal pseudo two-fold symmetry.^[13] Three gp45 molecules are tightly associated to form a closed ring encircling duplex DNA.

Gp45 sliding clamp, N-terminal

Identifiers

Symbol

DNA_pol_proc_fac

Available protein structures:
Pfam	structures
PDB	RCSB PDB; PDBe; PDBj
PDBsum	structure summary

Gp45 sliding clamp, C-terminal

Identifiers

Symbol

Gp45_slide_clamp_C

Available protein structures:
Pfam	structures
PDB	RCSB PDB; PDBe; PDBj
PDBsum	structure summary

Assembly

Sliding clamps are loaded onto their associated DNA template strands by specialized proteins known as "sliding clamp loaders", which also disassemble the clamps after replication has completed. The binding sites for these initiator proteins overlap with the binding sites for the DNA polymerase, so the clamp cannot simultaneously associate with a clamp loader and with a polymerase. Thus the clamp will not be actively disassembled while the polymerase remains bound. DNA clamps also associate with other factors involved in DNA and genome homeostasis, such as nucleosome assembly factors, Okazaki fragment ligases, and DNA repair proteins. All of these proteins also share a binding site on the DNA clamp that overlaps with the clamp loader site, ensuring that the clamp will not be removed while any enzyme is still working on the DNA. The activity of the clamp loader requires ATP hydrolysis to "close" the clamp around the DNA.

References

^ PDB 1W60; Kontopidis G, Wu SY, Zheleva DI, Taylor P, McInnes C, Lane DP, Fischer PM, Walkinshaw MD (February 2005). "Structural and biochemical studies of human proliferating cell nuclear antigen complexes provide a rationale for cyclin association and inhibitor design". Proc. Natl. Acad. Sci. U.S.A. 102 (6): 1871–6. doi:10.1073/pnas.0406540102. PMC 548533. PMID 15681588.
^ V. Mizrahi, R. N. Henrie, J. F. Marlier, K. A. Johnson, S. J. Benkovic (1985). "Rate-limiting steps in the DNA polymerase I reaction pathway". Biochemistry 24 (15): 4010–4018. doi:10.1021/bi00336a031.
^ ^a ^b Bruck I, O'Donnell M (2001). "The ring-type polymerase sliding clamp family". Genome Biol. 2 (1): REVIEWS3001. doi:10.1186/gb-2001-2-1-reviews3001. PMC 150441. PMID 11178284.
^ Matsumiya S, Ishino Y, Morikawa K (January 2001). "Crystal structure of an archaeal DNA sliding clamp: Proliferating cell nuclear antigen from Pyrococcus furiosus". Protein Sci. 10 (1): 17–23. doi:10.1110/ps.36401. PMC 2249843. PMID 11266590.
^ PDB 1MMI; Oakley AJ, Prosselkov P, Wijffels G, Beck JL, Wilce MC, Dixon NE (July 2003). "Flexibility revealed by the 1.85 Å crystal structure of the beta sliding-clamp subunit of Escherichia coli DNA polymerase III". Acta Crystallogr. D Biol. Crystallogr. 59 (Pt 7): 1192–9. doi:10.1107/S0907444903009958. PMID 12832762.
^ Lewin, Benjamin (1997). Genes VI. Oxford [Oxfordshire]: Oxford University Press. pp. 484–7. ISBN 0-19-857779-6.
^ Lehninger, Albert L (1975). Biochemistry: The Molecular Basis of Cell Structure and Function. New York: Worth Publishers. p. 894. ISBN 0-87901-047-9.
^ ^a ^b Stukenberg PT, Studwell-Vaughan PS, O'Donnell M (June 1991). "Mechanism of the sliding beta-clamp of DNA polymerase III holoenzyme". J. Biol. Chem. 266 (17): 11328–34. PMID 2040637.
^ Yin Z, Wang Y, Whittell LR, Jergic S, Liu M, Harry E, Dixon NE, Kelso MJ, Beck JL, Oakley AJ (2014). "DNA Replication Is the Target for the Antibacterial Effects of Nonsteroidal Anti-Inflammatory Drugs". Chemistry & Biology. doi:10.1016/j.chembiol.2014.02.009.
^ PDB 1AXC; Gulbis JM, Kelman Z, Hurwitz J, O'Donnell M, Kuriyan J (October 1996). "Structure of the C-terminal region of p21(WAF1/CIP1) complexed with human PCNA". Cell 87 (2): 297–306. doi:10.1016/S0092-8674(00)81347-1. PMID 8861913.
^ Suzuka I, Hata S, Matsuoka M, Kosugi S, Hashimoto J (January 1991). "Highly conserved structure of proliferating cell nuclear antigen (DNA polymerase delta auxiliary protein) gene in plants". Eur. J. Biochem. 195 (2): 571–5. doi:10.1111/j.1432-1033.1991.tb15739.x. PMID 1671766.
^ PDB 1CZD; Moarefi I, Jeruzalmi D, Turner J, O'Donnell M, Kuriyan J (March 2000). "Crystal structure of the DNA polymerase processivity factor of T4 bacteriophage". J. Mol. Biol. 296 (5): 1215–23. doi:10.1006/jmbi.1999.3511. PMID 10698628.
^ Steitz TA, Shamoo Y (1999). "Building a replisome from interacting pieces: sliding clamp complexed to a peptide from DNA polymerase and a polymerase editing complex". Cell 99 (2): 155–166. doi:10.1016/S0092-8674(00)81647-5. PMID 10535734.

External links

SCOP DNA clamp fold
CATH box architecture
clamp protein DnaN, E coli at the US National Library of Medicine Medical Subject Headings (MeSH)

DNA replication (comparing Prokaryotic to Eukaryotic)

Initiation

Prokaryotic (initiation)	Pre-replication complex dnaC Cdc6 Helicase dnaA dnaB T7 Primase dnaG

Eukaryotic (preparation in G1 phase)	Pre-replication complex Origin recognition complex ORC1 ORC2 ORC3 ORC4 ORC5 ORC6 Cdc6 Cdt1 Minichromosome maintenance MCM2 MCM3 MCM4 MCM5 MCM6 MCM7 Licensing factor Autonomously replicating sequence Single-strand binding protein SSBP2 SSBP3 SSBP4 RNase H RNASEH1 RNASEH2A Helicase: HFM1 Primase: PRIM1 PRIM2

Both	Origin of replication/Ori/Replicon Replication fork Lagging and leading strands Okazaki fragment Primer

Replication

Prokaryotic (elongation)	DNA polymerase III holoenzyme dnaC dnaE dnaH dnaN dnaQ dnaT dnaX holA holB holC holD holE Replisome DNA ligase DNA clamp Topoisomerase DNA gyrase Prokaryotic DNA polymerase: DNA polymerase I Klenow fragment

Eukaryotic (synthesis in S phase)	Replication factor C RFC1 Flap endonuclease FEN1 Topoisomerase Replication protein A RPA1 Eukaryotic DNA polymerase: delta POLD1 POLD2 POLD3 POLD4 DNA clamp PCNA

Both	Movement: Processivity DNA ligase

Termination

Telomere: Telomerase
- TERT
- TERC
- DKC1

See also: DNA replication and repair-deficiency disorder B bsyn: dna (repl, cycl, reco, repr) · tscr (fact, tcrg, nucl, rnat, rept, ptts) · tltn (risu, pttl, nexn) · dnab, rnab/runp · stru (domn, 1°, 2°, 3°, 4°)

v t e Protein tertiary structure

General	Structural domain Protein folding Structure determination methods

All-α folds:	Helix bundle Globin fold Homeodomain fold Alpha solenoid

All-β folds:	Immunoglobulin domain Beta barrel Beta-propeller

α/β folds:	TIM barrel Leucine-rich repeat Flavodoxin fold Rossmann fold Thioredoxin fold Trefoil knot fold

α+β folds:	DNA clamp Ferredoxin fold Ribonuclease A SH2-like fold

Irregular folds:	Conotoxin

←Secondary structure Quaternary structure→

This page is based on a Wikipedia article. The text is available under the Creative Commons Attribution/Share-Alike License.

This tab holds the annotation information that is stored in the Pfam database. As we move to using Wikipedia as our main source of annotation, the contents of this tab will be gradually replaced by the Wikipedia tab.

DNA polymerase III beta subunit, central domain Provide feedback

A dimer of the beta subunit of DNA polymerase beta forms a ring which encircles duplex DNA. Each monomer contains three domains of identical topology and DNA clamp fold.

Literature references

Kong XP, Onrust R, O'Donnell M, Kuriyan J; , Cell 1992;69:425-437.: Three-dimensional structure of the beta subunit of E. coli DNA polymerase III holoenzyme: a sliding DNA clamp. PUBMED:1349852 EPMC:1349852

Internal database links

SCOOP:	DNA_pol3_beta_3
Similarity to PfamA using HHSearch:	DNA_pol3_beta

External database links

PANDIT:	PF02767
Pseudofam:	PF02767
SCOP:	2pol
SYSTERS:	DNA_pol3_beta_2

This tab holds annotation information from the InterPro database.

InterPro entry IPR022637

This entry describes the central domain of the beta chain of DNA polymerase III. This is a complex, multichain enzyme responsible for most of the replicative synthesis in bacteria. The beta chain is required for initiation of replication from an RNA primer, nucleotide triphosphate (dNTP) residues being added to the 5'-end of the growing DNA chain.

Gene Ontology

The mapping between Pfam and Gene Ontology is provided by InterPro. If you use this data please cite InterPro.

Cellular component	DNA polymerase III complex (GO:0009360)
Molecular function	3'-5' exonuclease activity (GO:0008408)
	DNA-directed DNA polymerase activity (GO:0003887)
	DNA binding (GO:0003677)
Biological process	DNA replication (GO:0006260)

Domain organisation

Below is a listing of the unique domain organisations or architectures in which this domain is found. More...

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Pfam Clan

This family is a member of clan DNA_clamp (CL0060), which has the following description:

Sliding DNA clamps are ring-shaped proteins that allow DNA polymerase to achieve high processivity during chromosome replication by tethering the polymerase catalytic subunit to DNA. All of the structures share a 12-fold symmetry around the ring consisting of a simple structural repeat, though there is structural divergence in some of the repeats. Bacterial beta-clamps contain six repeats per subunit with two subunits per ring while the eukaryotic and bacteriophage clamps contain four repeats per subunit with three subunits per ring. Pairs of these repeats form a domain, which has been termed the 'processivity fold'; thus the ring of the sliding clamp contains six domains and therefore is often described as having 6-fold symmetry. A structural representative of a fourth family of processivity fold proteins, namely the herpes simplex virus UL42 protein, is also available. UL42 does not form a ring-shaped clamp, however, but rather functions as a monomer and interacts with DNA quite differently than do sliding clamps; it has been suggested that UL42 resembles a primitive ancestor of sliding clamps [2].

The clan contains the following 10 members:

DNA_pol3_beta DNA_pol3_beta_2 DNA_pol3_beta_3 DNA_PPF Herpes_UL42 Hus1 PCNA_C PCNA_N Rad1 Rad9

Alignments

We store a range of different sequence alignments for families. As well as the seed alignment from which the family is built, we provide the full alignment, generated by searching the sequence database using the family HMM. We also generate alignments using four representative proteomes (RP) sets, the NCBI sequence database, and our metagenomics sequence database. More...

There are various ways to view or download the sequence alignments that we store. We provide several sequence viewers and a plain-text Stockholm-format file for download.

Alignment types

We make a range of alignments for each Pfam-A family:

seed: the curated alignment from which the HMM for the family is built
full: the alignment generated by searching the sequence database using the HMM
RP15/RP35/RP55/RP75: Representative Proteomes (RPs) at 15%, 35%, 55% and 75% co-membership thresholds
NCBI: alignment generated by searching the NCBI sequence database using the family HMM
meta: alignment generated by searching the metagenomics sequence database using the family HMM

Viewing

You can see the alignments as HTML or in three different sequence viewers:

jalview: a Java applet developed at the University of Dundee. You will need Java installed before running jalview
HTML: an HTML page showing the whole alignment.Please note: full Pfam alignments can be very large. These HTML views are extremely large and often cause problems for browsers. Please use either jalview or the Pfam viewer if you have trouble viewing the HTML version
PP/Heatmap: an HTML-based representation of the alignment, coloured according to the posterior-probability (PP) values from the HMM. As for the standard HTML view, heatmap alignments can also be very large and slow to render.
Pfam viewer: an HTML-based viewer that uses DAS to retrieve alignment fragments on request

Reformatting

You can download (or view in your browser) a text representation of a Pfam alignment in various formats:

Selex
Stockholm
FASTA
MSF

You can also change the order in which sequences are listed in the alignment, change how insertions are represented, alter the characters that are used to represent gaps in sequences and, finally, choose whether to download the alignment or to view it in your browser directly.

Downloading

You may find that large alignments cause problems for the viewers and the reformatting tool, so we also provide all alignments in Stockholm format. You can download either the plain text alignment, or a gzipped version of it.

View options

We make a range of alignments for each Pfam-A family. You can see a description of each above. You can view these alignments in various ways but please note that some types of alignment are never generated while others may not be available for all families, most commonly because the alignments are too large to handle.

	Seed (15)	Full (4914)	Representative proteomes				NCBI (3844)	Meta (2795)
	Seed (15)	Full (4914)	RP15 (353)	RP35 (699)	RP55 (887)	RP75 (1035)	NCBI (3844)	Meta (2795)
Jalview	View	View	View	View	View	View	View	View
HTML	View	View	View	View	View	View
PP/heatmap	₁	View	View	View	View	View
Pfam viewer	View	View

¹Cannot generate PP/Heatmap alignments for seeds; no PP data available

Key: available, not generated, — not available.

Format an alignment

	Seed (15)	Full (4914)	Representative proteomes				NCBI (3844)	Meta (2795)
	Seed (15)	Full (4914)	RP15 (353)	RP35 (699)	RP55 (887)	RP75 (1035)	NCBI (3844)	Meta (2795)
Alignment:
Format:
Order:	Tree Alphabetical
Sequence:	Inserts lower case All upper case
Gaps:
Download/view:	Download View

Download options

We make all of our alignments available in Stockholm format. You can download them here as raw, plain text files or as gzip-compressed files.

	Seed (15)	Full (4914)	Representative proteomes				NCBI (3844)	Meta (2795)
	Seed (15)	Full (4914)	RP15 (353)	RP35 (699)	RP55 (887)	RP75 (1035)	NCBI (3844)	Meta (2795)
Raw Stockholm	Download	Download	Download	Download	Download	Download	Download	Download
Gzipped	Download	Download	Download	Download	Download	Download	Download	Download

You can also download a FASTA format file containing the full-length sequences for all sequences in the full alignment.

External links

MyHits provides a collection of tools to handle multiple sequence alignments. For example, one can refine a seed alignment (sequence addition or removal, re-alignment or manual edition) and then search databases for remote homologs using HMMER3.

HMM logo

HMM logos is one way of visualising profile HMMs. Logos provide a quick overview of the properties of an HMM in a graphical form. You can see a more detailed description of HMM logos and find out how you can interpret them here. More...

Trees

This page displays the phylogenetic tree for this family's seed alignment. We use FastTree to calculate neighbour join trees with a local bootstrap based on 100 resamples (shown next to the tree nodes). FastTree calculates approximately-maximum-likelihood phylogenetic trees from our seed alignment.

Note: You can also download the data file for the tree.

Curation and family details

This section shows the detailed information about the Pfam family. You can see the definitions of many of the terms in this section in the glossary and a fuller explanation of the scoring system that we use in the scores section of the help pages.

Curation

Seed source:

Pfam-B_631 (release 2.1)

Previous IDs:

none

Type:

Domain

Author:

Bateman A, Griffiths-Jones SR

Number in seed:

15

Number in full:

4914

Average length of the domain:

115.90 aa

Average identity of full alignment:

30 %

Average coverage of the sequence by the domain:

31.47 %

HMM information

HMM build commands:

build method: hmmbuild -o /dev/null HMM SEED

search method: hmmsearch -Z 23193494 -E 1000 --cpu 4 HMM pfamseq

Model details:

Parameter	Sequence	Domain
Gathering cut-off	20.5	20.5
Trusted cut-off	20.5	20.5
Noise cut-off	20.4	20.4

Model length:

116

Family (HMM) version:

11

Download:

download the raw HMM for this family

Species distribution

Sunburst
Tree

Sunburst controls

Show

This visualisation provides a simple graphical representation of the distribution of this family across species. You can find the original interactive tree in the adjacent tab. More...

This chart is a modified "sunburst" visualisation of the species tree for this family. It shows each node in the tree as a separate arc, arranged radially with the superkingdoms at the centre and the species arrayed around the outermost ring.

How the sunburst is generated

The tree is built by considering the taxonomic lineage of each sequence that has a match to this family. For each node in the resulting tree, we draw an arc in the sunburst. The radius of the arc, its distance from the root node at the centre of the sunburst, shows the taxonomic level ("superkingdom", "kingdom", etc). The length of the arc represents either the number of sequences represented at a given level, or the number of species that are found beneath the node in the tree. The weighting scheme can be changed using the sunburst controls.

In order to reduce the complexity of the representation, we reduce the number of taxonomic levels that we show. We consider only the following eight major taxonomic levels:

superkingdom
kingdom
phylum
class
order
family
genus
species

Colouring and labels

Segments of the tree are coloured approximately according to their superkingdom. For example, archeal branches are coloured with shades of orange, eukaryotes in shades of purple, etc. The colour assignments are shown under the sunburst controls. Where space allows, the name of the taxonomic level will be written on the arc itself.

As you move your mouse across the sunburst, the current node will be highlighted. In the top section of the controls panel we show a summary of the lineage of the currently highlighed node. If you pause over an arc, a tooltip will be shown, giving the name of the taxonomic level in the title and a summary of the number of sequences and species below that node in the tree.

Anomalies in the taxonomy tree

There are some situations that the sunburst tree cannot easily handle and for which we have work-arounds in place.

Missing taxonomic levels

Some species in the taxonomic tree may not have one or more of the main eight levels that we display. For example, Bos taurus is not assigned an order in the NCBI taxonomic tree. In such cases we mark the omitted level with, for example, "No order", in both the tooltip and the lineage summary.

Unmapped species names

The tree is built by looking at each sequence in the full alignment for the family. We take the name of the species given by UniProt and try to map that to the full taxonomic tree from NCBI. In some cases, the name chosen by UniProt does not map to any node in the NCBI tree, perhaps because the chosen name is listed as a synonym or a misspelling in the NCBI taxonomy.

So that these nodes are not simply omitted from the sunburst tree, we group them together in a separate branch (or segment of the sunburst tree). Since we cannot determine the lineage for these unmapped species, we show all levels between the superkingdom and the species as "uncategorised".

Sub-species

Since we reduce the species tree to only the eight main taxonomic levels, sequences that are mapped to the sub-species level in the tree would not normally be shown. Rather than leave out these species, we map them instead to their parent species. So, for example, for sequences belonging to one of the Vibrio cholerae sub-species in the NCBI taxonomy, we show them instead as belonging to the species Vibrio cholerae.

Too many species/sequences

For large species trees, you may see blank regions in the outer layers of the sunburst. These occur when there are large numbers of arcs to be drawn in a small space. If an arc is less than approximately one pixel wide, it will not be drawn and the space will be left blank. You may still be able to get some information about the species in that region by moving your mouse across the area, but since each arc will be very small, it will be difficult to accurately locate a particular species.

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Tree controls

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The tree shows the occurrence of this domain across different species. More...

Species trees

We show the species tree in one of two ways. For smaller trees we try to show an interactive representation, which allows you to select specific nodes in the tree and view them as an alignment or as a set of Pfam domain graphics.

Unfortunately we have found that there are problems viewing the interactive tree when the it becomes larger than a certain limit. Furthermore, we have found that Internet Explorer can become unresponsive when viewing some trees, regardless of their size. We therefore show a text representation of the species tree when the size is above a certain limit or if you are using Internet Explorer to view the site.

If you are using IE you can still load the interactive tree by clicking the "Generate interactive tree" button, but please be aware of the potential problems that the interactive species tree can cause.

Interactive tree

For all of the domain matches in a full alignment, we count the number that are found on all sequences in the alignment. This total is shown in the purple box.

We also count the number of unique sequences on which each domain is found, which is shown in green. Note that a domain may appear multiple times on the same sequence, leading to the difference between these two numbers.

Finally, we group sequences from the same organism according to the NCBI code that is assigned by UniProt, allowing us to count the number of distinct sequences on which the domain is found. This value is shown in the pink boxes.

We use the NCBI species tree to group organisms according to their taxonomy and this forms the structure of the displayed tree. Note that in some cases the trees are too large (have too many nodes) to allow us to build an interactive tree, but in most cases you can still view the tree in a plain text, non-interactive representation. Those species which are represented in the seed alignment for this domain are highlighted.

You can use the tree controls to manipulate how the interactive tree is displayed:

show/hide the summary boxes
highlight species that are represented in the seed alignment
expand/collapse the tree or expand it to a given depth
select a sub-tree or a set of species within the tree and view them graphically or as an alignment
save a plain text representation of the tree

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Interactions

There are 3 interactions for this family. More...

DNA_pol3_delta DNA_pol3_beta_3 DNA_pol3_beta

Structures

For those sequences which have a structure in the Protein DataBank, we use the mapping between UniProt, PDB and Pfam coordinate systems from the PDBe group, to allow us to map Pfam domains onto UniProt sequences and three-dimensional protein structures. The table below shows the structures on which the DNA_pol3_beta_2 domain has been found. There are 54 instances of this domain found in the PDB. Note that there may be multiple copies of the domain in a single PDB structure, since many structures contain multiple copies of the same protein seqence.

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Archea	Eukaryota
Bacteria	Other sequences
Viruses	Unclassified
Viroids	Unclassified sequence

Family: DNA_pol3_beta_2 (PF02767)

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Summary: DNA polymerase III beta subunit, central domain

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Contents

Structure

Bacterial

As a drug target

Eukaryote

Viral

Assembly

References

Further reading

External links

DNA polymerase III beta subunit, central domain Provide feedback

Literature references

Internal database links

External database links

InterPro entry IPR022637

Gene Ontology

Domain organisation

Pfam Clan

Alignments

Alignment types

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External links

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Trees

Curation and family details

Curation

HMM information

Species distribution

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Colour assignments

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Anomalies in the taxonomy tree

Missing taxonomic levels

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Annotation

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Selected sequences

Species trees

Interactive tree

Interactions

Structures