title: Holliday junction resolution in human cells: two junction endonucleases with distinct substrate specificities.
abstract: Enzymatic activities that cleave Holliday junctions are required for the resolution of recombination intermediates and for the restart of stalled replication forks. Here we show that human cell-free extracts possess two distinct endonucleases that can cleave Holliday junctions. The first cleaves Holliday junctions in a structure- and sequence-specific manner, and associates with an ATP-dependent branch migration activity. Together, these activities promote branch migration/resolution reactions similar to those catalysed by the Escherichia coli RuvABC resolvasome. Like RuvC-mediated resolution, the products can be religated. The second, containing Mus81 protein, cuts Holliday junctions but the products are mostly non-ligatable. Each nuclease has a defined substrate specificity: the branch migration-associated resolvase is highly specific for Holliday junctions, whereas the Mus81-associated endonuclease is one order of magnitude more active upon replication fork and 3'-flap structures. Thus, both nucleases are capable of cutting Holliday junctions formed during recombination or through the regression of stalled replication forks. However, the Mus81-associated endonuclease may play a more direct role in replication fork collapse by catalysing the cleavage of stalled fork structures.
authors.affiliation: Cancer Research UK, London Research Institute, Clare Hall Laboratories, South Mimms, Hertfordshire EN6 3LD, UK.
authors.forename: Angelos
authors.initials: A
authors.lastname: Constantinou
authors.forename: Xiao-Bo
authors.initials: XB
authors.lastname: Chen
authors.forename: Clare H
authors.initials: CH
authors.lastname: McGowan
authors.forename: Stephen C
authors.initials: SC
authors.lastname: West
mesh_terms: D001483:Base Sequence; D002474:Cell-Free System; D004247:DNA / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004706:Endodeoxyribonucleases / Q000378:metabolism*; D004720:Endonucleases; D006367:HeLa Cells; D045565:Holliday Junction Resolvases; D006801:Humans; D066298:In Vitro Techniques; D008954:Models, Biological; D009692:Nucleic Acid Heteroduplexes / Q000737:chemistry / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D004268:DNA-Binding Proteins; D009692:Nucleic Acid Heteroduplexes; D004247:DNA; D004706:Endodeoxyribonucleases; D004720:Endonucleases; C498772:MUS81 protein, human; D045565:Holliday Junction Resolvases