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Escherichia coli endonuclease III (EC 184.108.40.206) (gene nth)  is a DNA
repair enzyme that acts both as a DNA N-glycosylase, removing oxidized
pyrimidines from DNA, and as an apurinic/apyrimidinic (AP) endonuclease,
introducing a single-strand nick at the site from which the damaged base was
removed. Endonuclease III is an iron-sulfur protein that binds a single 4Fe-4S
cluster. The 4Fe-4S cluster does not seem to be important for catalytic
activity, but is probably involved in the proper positioning of the enzyme
along the DNA strand .
Endonuclease III is evolutionary related to the following proteins:
Fission yeast endonuclease III homolog (gene nth1) .
Escherichia coli and related protein DNA repair protein mutY, which is an
adenine glycosylase. MutY is a larger protein (350 amino acids) than
endonuclease III (211 amino acids).
Micrococcus luteus ultraviolet N-glycosylase/AP lyase which initiates
repair at cis-syn pyrimidine dimers.
ORF10 in plasmid pFV1 of the thermophilic archaebacteria Methanobacterium
thermoformicicum . Restriction methylase m.MthTI, which is encoded by
this plasmid, generates 5-methylcytosine which is subject to deamination
resulting in G-T mismatches. This protein could correct these mismatches.
Yeast hypothetical protein YAL015c.
Fission yeast hypothetical protein SpAC26A3.02.
Caenorhabditis elegans hypothetical protein R10E4.5.
Methanococcus jannaschii hypothetical protein MJ0613.
The 4Fe-4S cluster is bound by four cysteines which are all located in a 17
amino acid region at the C-terminal end of endonuclease III. A similar region
is also present in the central section of mutY and in the C-terminus of ORF10
and of the Micrococcus UV endonuclease. The 4Fe-4S cluster region does not
exist in YAL015c.
We developed two signature patterns for these proteins: the first corresponds
to the core of the iron-sulfur binding domain, the second corresponds to the
best conserved region in the catalytic core of these enzymes.
December 2004 / Pattern and text revised.
PROSITE methods (with tools and information) covered by this documentation:
Kuo C.-F., McRee D.E., Fisher C.L., O'Handley S.F., Cunningham R.P., Tainer J.A.
Atomic structure of the DNA repair [4Fe-4S] enzyme endonuclease III.
Noelling J., van Eeden F.J.M., Eggen R.I.L., de Vos W.M.
Nucleic Acids Res. 20:6501-6507(1992).
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