Summary

Restriction endonuclease FokI, catalytic domain

No Pfam abstract.

Literature references

Wah DA, Bitinaite J, Schildkraut I, Aggarwal AK; , Proc Natl Acad Sci U S A. 1998;95:10564-10569.: Structure of FokI has implications for DNA cleavage. PUBMED:9724743
Kovall RA, Matthews BW; , Curr Opin Chem Biol 1999;3:578-583.: Type II restriction endonucleases: structural, functional and evolutionary relationships. PUBMED:10508668

InterPro entry IPR004233

Type II restriction endonucleases () are components of prokaryotic DNA restriction-modification mechanisms that protect the organism against invading foreign DNA. These site-specific deoxyribonucleases catalyse the endonucleolytic cleavage of DNA to give specific double-stranded fragments with terminal 5'-phosphates. Of the 3000 restriction endonucleases that have been characterised, most are homodimeric or tetrameric enzymes that cleave target DNA at sequence-specific sites close to the recognition site. For homodimeric enzymes, the recognition site is usually a palindromic sequence 4-8 bp in length. Most enzymes require magnesium ions as a cofactor for catalysis. Although they can vary in their mode of recognition, many restriction endonucleases share a similar structural core comprising four beta-strands and one alpha-helix, as well as a similar mechanism of cleavage, suggesting a common ancestral origin PUBMED:15770420. However, there is still considerable diversity amongst restriction endonucleases PUBMED:14576294, PUBMED:11827971. The target site recognition process triggers large conformational changes of the enzyme and the target DNA, leading to the activation of the catalytic centres. Like other DNA binding proteins, restriction enzymes are capable of non-specific DNA binding as well, which is the prerequisite for efficient target site location by facilitated diffusion. Non-specific binding usually does not involve interactions with the bases but only with the DNA backbone PUBMED:11557805.

There are four classes of restriction endonucleases: types I, II,III and IV. All types of enzymes recognise specific short DNA sequences and carry out the endonucleolytic cleavage of DNA to give specific double-stranded fragments with terminal 5'-phosphates. They differ in their recognition sequence, subunit composition, cleavage position, and cofactor requirements PUBMED:15121719, PUBMED:12665693, as summarised below:

Type I enzymes () cleave at sites remote from recognition site; require both ATP and S-adenosyl-L-methionine to function; multifunctional protein with both restriction and methylase () activities.
Type II enzymes () cleave within or at short specific distances from recognition site; most require magnesium; single function (restriction) enzymes independent of methylase.
Type III enzymes () cleave at sites a short distance from recognition site; require ATP (but doesn't hydrolyse it); S-adenosyl-L-methionine stimulates reaction but is not required; exists as part of a complex with a modification methylase methylase ().
Type IV enzymes target methylated DNA.

Thie entry represents the type IIS restriction endonuclease FokI (), which is a member of an unusual class of bipartite restriction enzymes that recognise a specific DNA sequence and cleave DNA nonspecifically a short distance away from that sequence PUBMED:9724744. FokI contains amino- and carboxy-terminal domains corresponding to the DNA-recognition () and cleavage functions, respectively.

The catalytic domain contains only a single catalytic centre, raising the question of how monomeric FokI manages to cleave both DNA strands. The catalytic domain is sequestered in a 'piggyback' fashion by the recognition domain PUBMED:9214510.

Gene Ontology

Molecular function	DNA binding (GO:0003677)
Molecular function	Type II site-specific deoxyribonuclease activity (GO:0009036)
Biological process	DNA restriction-modification system (GO:0009307)

External database links

PANDIT:	PF02980
SCOP:	2fok
SYSTERS:	FokI_C

Domain organisation

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

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Alignments

There are various ways to view or download the sequence alignments that we store. You can use a sequence viewer to look at either the seed or full alignment for the family, or you can look at a plain text version of the sequence in a variety of different formats. More...

View options

Alignment:	Seed (4) Full (7) NCBI (7) Metagenomics
Viewer:

Formatting options

Alignment:	Seed (4) Full (7)
Format:
Order:	Tree Alphabetical
Sequence:	Inserts lower case All upper case
Gaps:
Download/view:	Download View

Download options

Very large alignments can often cause problems for the formatting tool above. If you find that downloading or viewing a large alignment is problematic, you can also download a gzip-compressed, Stockholm-format file containing the seed or full alignment for this family.

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

The main seed and full alignments are generated using sequences from the UniProt sequence database. However, we also generate alignments using sequences from the NCBI sequence database and the "metaseq" metagenomics dataset.

You can view alignments from these two additional datasets using the form above, or you can download alignments of NCBI or metagenomics sequences, as gzip-compressed files.

Pfam alignments:	Seed (4) Full (7) NCBI (7) Metagenomics
Full length sequences	Full-sequences (7)

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 HMMER2.

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. 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 or full alignments.

Note: You can also download the data files for the seed, full, NCBI or metagenomics trees.

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:

Structural domain

Previous IDs:

none

Type:

Domain

Author:

Griffiths-Jones SR

Number in seed:

4

Number in full:

7

Average length of the domain:

136.10 aa

Average identity of full alignment:

47 %

Average coverage of the sequence by the domain:

25.39 %

HMM information

HMM build commands:

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

search method: hmmsearch -Z 9421015 -E 1000 HMM pfamseq

Model details:

Parameter	Sequence	Domain
Gathering cut-off	25.0	25.0
Trusted cut-off	163.8	162.4
Noise cut-off	19.2	18.8

Model length:

142

Family (HMM) version:

9

Download:

download the raw HMM for this family

Species distribution

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
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Interactions

There is 1 interaction for this family. More...

Endonuc-FokI_C

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 MSD 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 FokI_C domain has been found.

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Family: FokI_C (PF02980)

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