title: Metnase Mediates Loading of Exonuclease 1 onto Single Strand Overhang DNA for End Resection at Stalled Replication Forks.
abstract: Stalling at DNA replication forks generates stretches of single-stranded (ss) DNA on both strands that are exposed to nucleolytic degradation, potentially compromising genome stability. One enzyme crucial for DNA replication fork repair and restart of stalled forks in human is Metnase (also known as SETMAR), a chimeric fusion protein consisting of a su(var)3-9, enhancer-of-zeste and trithorax (SET) histone methylase and transposase nuclease domain. We previously showed that Metnase possesses a unique fork cleavage activity necessary for its function in replication restart and that its SET domain is essential for recovery from hydroxyurea-induced DNA damage. However, its exact role in replication restart is unclear. In this study, we show that Metnase associates with exonuclease 1 (Exo1), a 5'-exonuclease crucial for 5'-end resection to mediate DNA processing at stalled forks. Metnase DNA cleavage activity was not required for Exo1 5'-exonuclease activity on the lagging strand daughter DNA, but its DNA binding activity mediated loading of Exo1 onto ssDNA overhangs. Metnase-induced enhancement of Exo1-mediated DNA strand resection required the presence of these overhangs but did not require Metnase's DNA cleavage activity. These results suggest that Metnase enhances Exo1-mediated exonuclease activity on the lagging strand DNA by facilitating Exo1 loading onto a single strand gap at the stalled replication fork.
authors.affiliation: From the Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana 46202.
authors.forename: Hyun-Suk
authors.initials: HS
authors.lastname: Kim
authors.affiliation: the Department of Medicine, University of Florida and Shands Health Care System, Gainesville, Florida 32610, and.
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Williamson
authors.affiliation: the Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, Colorado 80523.
authors.forename: Jac A
authors.initials: JA
authors.lastname: Nickoloff
authors.affiliation: the Department of Medicine, University of Florida and Shands Health Care System, Gainesville, Florida 32610, and.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Hromas
authors.affiliation: From the Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana 46202, slee@iu.edu.
authors.forename: Suk-Hee
authors.initials: SH
authors.lastname: Lee
mesh_terms: D004249:DNA Damage; D045643:DNA Repair Enzymes / Q000235:genetics / Q000378:metabolism*; D004261:DNA Replication; D004277:DNA, Single-Stranded / Q000235:genetics / Q000378:metabolism*; D005090:Exodeoxyribonucleases / Q000235:genetics / Q000378:metabolism*; D057809:HEK293 Cells; D011495:Histone-Lysine N-Methyltransferase / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D006918:Hydroxyurea / Q000009:adverse effects / Q000494:pharmacology
chemical_list: D004277:DNA, Single-Stranded; D011495:Histone-Lysine N-Methyltransferase; C510450:SETMAR protein, human; C114331:EXO1 protein, human; D005090:Exodeoxyribonucleases; D045643:DNA Repair Enzymes; D006918:Hydroxyurea
keywords: DNA damage; DNA enzyme; DNA repair; DNA replication; DNA-binding protein