Organization of the BcgI restriction-modification protein for the transfer of one methyl group to DNA

Rachel M. Smith, Alistair J. Jacklin, Jacqui J T Marshall, Frank Sobott, Stephen E. Halford*

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)

7 Citations (Scopus)

Abstract

The Type IIB restriction-modification 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 A(2)B 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 N-6-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 A(2)B protomers, which indicates that it requires an assembly containing at least two A(2)B units.

Original languageEnglish
Pages (from-to)405-417
Number of pages13
JournalNucleic Acids Research
Volume41
Issue number1
DOIs
Publication statusPublished - Jan 2013

Keywords

  • 2 RECOGNITION SITES
  • MODIFICATION SYSTEM
  • ESCHERICHIA-COLI
  • MASS-SPECTROMETRY
  • METHYLTRANSFERASES
  • ENDONUCLEASE
  • ENZYMES
  • PURIFICATION
  • CLEAVAGE
  • NOMENCLATURE

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