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Title
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Monomeric Restriction Endonuclease BcnI in the Apo Form and in an Asymmetric Complex with Target DNA.
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Authors
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M.Sokolowska,
M.Kaus-Drobek,
H.Czapinska,
G.Tamulaitis,
R.H.Szczepanowski,
C.Urbanke,
V.Siksnys,
M.Bochtler.
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Ref.
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J Mol Biol, 2007,
369,
722-734.
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PubMed id
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Abstract
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Restriction endonuclease BcnI cleaves duplex DNA containing the sequence CC/SGG
(S stands for C or G, / designates a cleavage position) to generate staggered
products with single nucleotide 5'-overhangs. Here, we show that BcnI functions
as a monomer that interacts with its target DNA in 1:1 molar ratio and report
crystal structures of BcnI in the absence and in the presence of DNA. In the
complex with DNA, BcnI makes specific contacts with all five bases of the target
sequence and not just with a half-site, as the protomer of a typical dimeric
restriction endonuclease. Our data are inconsistent with BcnI dimerization and
suggest that the enzyme introduces double-strand breaks by sequentially nicking
individual DNA strands, although this remains to be confirmed by kinetic
experiments. BcnI is remotely similar to the DNA repair protein MutH and shares
approximately 20% sequence identity with the restriction endonuclease MvaI,
which is specific for the related sequence CC/WGG (W stands for A or T). As
expected, BcnI is structurally similar to MvaI and recognizes conserved bases in
the target sequence similarly but not identically. BcnI has a unique machinery
for the recognition of the central base-pair.
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