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Title
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Organization of the BcgI restriction-modification protein for the transfer of one methyl group to DNA
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Author
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Abstract
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| The Type IIB restrictionmodification protein BcgI contains A and B subunits in a 2:1 ratio: A has the active sites for both endonuclease and methyltransferase functions while B recognizes the DNA. Like almost all Type IIB systems, BcgI needs two unmethylated sites for nuclease activity; it cuts both sites upstream and downstream of the recognition sequence, hydrolyzing eight phosphodiester bonds in a single synaptic complex. This complex may incorporate four A2B protomers to give the eight catalytic centres (one per A subunit) needed to cut all eight bonds. The BcgI recognition sequence contains one adenine in each strand that can be N6-methylated. Although most DNA methyltransferases operate at both unmethylated and hemi-methylated sites, BcgI methyltransferase is only effective at hemi-methylated sites, where the nuclease component is inactive. Unlike the nuclease, the methyltransferase acts at solitary sites, functioning catalytically rather than stoichiometrically. Though it transfers one methyl group at a time, presumably through a single A subunit, BcgI methyltransferase can be activated by adding extra A subunits, either individually or as part of A2B protomers, which indicates that it requires an assembly containing at least two A2B units. |
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Language
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English
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Source (journal)
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Nucleic acids research. - London
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Publication
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London
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2013
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ISSN
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0305-1048
1362-4962
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DOI
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10.1093/NAR/GKS1000
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Volume/pages
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41
:1
(2013)
, p. 405-417
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ISI
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000312889900065
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Full text (Publisher's DOI)
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Full text (open access)
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