Dissection of the sequence specificity of the Holliday junction endonuclease CCE1

M J Schofield, D M J Lilley, Malcolm F White

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42 Citations (Scopus)

Abstract

CCEI is a Holliday (four-way DNA) junction-specific endonuclease which resolves mitochondrial DNA recombination intermediates in Saccharomyces cerevisiae. The junction-resolving enzymes are a diverse class, widely distributed in nature from viruses to higher eukaryotes. In common with most other junction-resolving enzymes, the cleavage activity of CCE1 is nucleotide sequence-dependent. We have undertaken a systematic study of the sequence specificity of CCE1, using a single turnover kinetic assay and a panel of synthetic four-way DNA junction substrates. A tetranucleotide consensus cleavage sequence 5'-ACT down arrow A has been identified, with specificity residing mainly at the central CT dinucleotide. Equilibrium constants for CCE1 binding to four-way junctions are unaffected by sequence variations, suggesting that substrate discrimination occurs predominantly in the transition state complex. CCE1 cuts most efficiently at the junction center, but can also cleave the DNA backbone at positions one nucleotide 3' or 5' of the point of strand exchange, suggesting a significant degree of conformational flexibility in the CCE1:junction complex. Introduction of base analogues at single sites in four-way junctions has allowed investigation of the sequence specificity of CCE1 in finer detail. In particular, the N7 moiety of the guanine base-pairing with the cytosine of the consensus sequence appears to be crucial for catalysis. The functional significance of sequence specificity in junction-resolving enzymes is discussed.

Original languageEnglish
Pages (from-to)7733-7740
Number of pages8
JournalBiochemistry
Volume37
Issue number21
Publication statusPublished - 26 May 1998

Keywords

  • DEGENERATE RECOGNITION SEQUENCES
  • CRUCIFORM CUTTING ENDONUCLEASE
  • RESTRICTION-ENDONUCLEASE
  • GENETIC-RECOMBINATION
  • ESCHERICHIA-COLI
  • DNA
  • YEAST
  • IDENTIFICATION
  • ACCURACY
  • CLEAVAGE

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