title: Human exonuclease 5 is a novel sliding exonuclease required for genome stability.
abstract: Previously, we characterized Saccharomyces cerevisiae exonuclease 5 (EXO5), which is required for mitochondrial genome maintenance. Here, we identify the human homolog (C1orf176; EXO5) that functions in the repair of nuclear DNA damage. Human EXO5 (hEXO5) contains an iron-sulfur cluster. It is a single-stranded DNA (ssDNA)-specific bidirectional exonuclease with a strong preference for 5'-ends. After loading at an ssDNA end, hEXO5 slides extensively along the ssDNA prior to cutting, hence the designation sliding exonuclease. However, the single-stranded binding protein human replication protein A (hRPA) restricts sliding and enforces a unique, species-specific 5'-directionality onto hEXO5. This specificity is lost with a mutant form of hRPA (hRPA-t11) that fails to interact with hEXO5. hEXO5 localizes to nuclear repair foci in response to DNA damage, and its depletion in human cells leads to an increased sensitivity to DNA-damaging agents, in particular interstrand cross-linking-inducing agents. Depletion of hEXO5 also results in an increase in spontaneous and damage-induced chromosome abnormalities including the frequency of triradial chromosomes, suggesting an additional defect in the resolution of stalled DNA replication forks in hEXO5-depleted cells.
authors.affiliation: Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
authors.forename: Justin L
authors.initials: JL
authors.lastname: Sparks
authors.forename: Rakesh
authors.initials: R
authors.lastname: Kumar
authors.forename: Mayank
authors.initials: M
authors.lastname: Singh
authors.forename: Marc S
authors.initials: MS
authors.lastname: Wold
authors.forename: Tej K
authors.initials: TK
authors.lastname: Pandita
authors.forename: Peter M
authors.initials: PM
authors.lastname: Burgers
mesh_terms: D000595:Amino Acid Sequence; D055162:Biocatalysis / Q000187:drug effects / Q000528:radiation effects; D002869:Chromosome Aberrations / Q000187:drug effects / Q000528:radiation effects; D017124:Conserved Sequence; D003432:Cross-Linking Reagents / Q000494:pharmacology; D004260:DNA Repair / Q000187:drug effects / Q000528:radiation effects; D004277:DNA, Single-Stranded / Q000378:metabolism; D005092:Exonucleases / Q000737:chemistry / Q000378:metabolism*; D015894:Genome, Human / Q000235:genetics*; D042822:Genomic Instability / Q000187:drug effects / Q000528:radiation effects; D006801:Humans; D007506:Iron-Sulfur Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D011485:Protein Binding / Q000187:drug effects / Q000528:radiation effects; D055503:Protein Multimerization / Q000187:drug effects / Q000528:radiation effects; D051716:Replication Protein A / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity / Q000187:drug effects / Q000528:radiation effects; D014466:Ultraviolet Rays
chemical_list: D003432:Cross-Linking Reagents; D004277:DNA, Single-Stranded; D007506:Iron-Sulfur Proteins; C497167:RPA1 protein, human; D051716:Replication Protein A; C578285:EXO5 protein, human; D005092:Exonucleases