Organization of the BcgI restriction-modification protein for the cleavage of eight phosphodiester bonds in DNA

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

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

10 Citations (Scopus)

Abstract

Type IIB restriction-modification systems, such as BcgI, feature a single protein with both endonuclease and methyltransferase activities. Type IIB nucleases require two recognition sites and cut both strands on both sides of their unmodified sites. BcgI cuts all eight target phosphodiester bonds before dissociation. The BcgI protein contains A and B polypeptides in a 2:1 ratio: A has one catalytic centre for each activity; B recognizes the DNA. We show here that BcgI is organized as A(2)B protomers, with B at its centre, but that these protomers self-associate to assemblies containing several A(2)B units. Moreover, like the well known FokI nuclease, BcgI bound to its site has to recruit additional protomers before it can cut DNA. DNA-bound BcgI can alternatively be activated by excess A subunits, much like the activation of FokI by its catalytic domain. Eight A subunits, each with one centre for nuclease activity, are presumably needed to cut the eight bonds cleaved by BcgI. Its nuclease reaction may thus involve two A(2)B units, each bound to a recognition site, with two more A(2)B units bridging the complexes by protein-protein interactions between the nuclease domains.

Original languageEnglish
Pages (from-to)391-404
Number of pages14
JournalNucleic Acids Research
Volume41
Issue number1
DOIs
Publication statusPublished - Jan 2013

Keywords

  • 2 RECOGNITION SITES
  • MODIFICATION SYSTEM
  • SINGLE POLYPEPTIDE
  • BINDING SITES
  • ENDONUCLEASE
  • FOKI
  • ENZYMES
  • MECHANISM
  • METHYLTRANSFERASES
  • COPIES

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