Exonuclease III

Exonuclease III

Protein
Name=Exonuclease III
Symbol=?
AltSymbols=ExoIII
HGNCid=N/A
Chromosome=N/A
Arm=
Band=
LocusSupplementaryData=
ECnumber=3.1.11.2
OMIM=N/A
EntrezGene=?
RefSeq=?
UniProt=P09030

Exonuclease III (ExoIII) is an enzyme that belongs to the exonuclease family. ExoIII catalyzes the stepwise removal of mononucleotides from 3´-hydroxyl termini of duplex DNA [1] . A limited number of nucleotides are removed during each binding event, resulting in coordinated progressive deletions within the population of DNA molecules [2] .

Function

The preferred substrates are blunt or recessed 3´-termini, although ExoIII also acts at nicks in duplex DNA to produce single-strand gaps. The enzyme is not active on single-stranded DNA, and thus 3´-protruding termini are resistant to cleavage. The degree of resistance depends on the length of the extension, with extensions 4 bases or longer being essentially resistant to cleavage. This property is used to produce unidirectional deletions from a linear molecule with one resistant (3´-overhang) and one susceptible (blunt or 5´-overhang) terminus [3] .

ExoIII activity depends partially on the DNA helical structure [4] and displays sequence dependence (C>A=T>G) [5] .

ExoIII has also been reported to have RNase H, 3´-phosphatase and AP-endonuclease activities [1] .

Regulation

Temperature, salt concentration and the ratio of enzyme to DNA greatly affect enzyme activity, requiring reaction conditions to be tailored to specific applications.

References

#Exonuclease III of Escherichia coli K-12, an AP endonuclease. "Methods Enzymol. 1980; 65: 201-11."
#Molecular Cloning: A Laboratory Manual. "1989, 2nd. Ed., 5.84-5.85."
#Unidirectional digestion with exonuclease III creates targeted breakpoints for DNA sequencing. "Gene. 1984; 28: 351-9" [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=6235151&query_hl=21&itool=pubmed_docsum Abstract]
#A deoxyribonucleic acid phosphatase-exonuclease from Escherichia coli. II. Characterization of the exonuclease activity. "J Biol Chem. 1964; 239: 251-8" [http://www.jbc.org/cgi/reprint/239/1/251 Free text (PDF - 937KB)]
#Sequence specificity of exonuclease III from E. coli. "Nucleic Acids Res. 1982; 10: 4845-59." [http://www.pubmedcentral.gov/articlerender.fcgi?tool=pubmed&pubmedid=6752885 Free text]


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