title: Mammalian Exo1 encodes both structural and catalytic functions that play distinct roles in essential biological processes.
abstract: Mammalian Exonuclease 1 (EXO1) is an evolutionarily conserved, multifunctional exonuclease involved in DNA damage repair, replication, immunoglobulin diversity, meiosis, and telomere maintenance. It has been assumed that EXO1 participates in these processes primarily through its exonuclease activity, but recent studies also suggest that EXO1 has a structural function in the assembly of higher-order protein complexes. To dissect the enzymatic and nonenzymatic roles of EXO1 in the different biological processes in vivo, we generated an EXO1-E109K knockin (Exo1(EK)) mouse expressing a stable exonuclease-deficient protein and, for comparison, a fully EXO1-deficient (Exo1(null)) mouse. In contrast to Exo1(null/null) mice, Exo1(EK/EK) mice retained mismatch repair activity and displayed normal class switch recombination and meiosis. However, both Exo1-mutant lines showed defects in DNA damage response including DNA double-strand break repair (DSBR) through DNA end resection, chromosomal stability, and tumor suppression, indicating that the enzymatic function is required for those processes. On a transformation-related protein 53 (Trp53)-null background, the DSBR defect caused by the E109K mutation altered the tumor spectrum but did not affect the overall survival as compared with p53-Exo1(null) mice, whose defects in both DSBR and mismatch repair also compromised survival. The separation of these functions demonstrates the differential requirement for the structural function and nuclease activity of mammalian EXO1 in distinct DNA repair processes and tumorigenesis in vivo.
authors.affiliation: Department of Cell Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
authors.forename: Sonja
authors.initials: S
authors.lastname: Schaetzlein
authors.forename: Richard
authors.initials: R
authors.lastname: Chahwan
authors.forename: Elena
authors.initials: E
authors.lastname: Avdievich
authors.forename: Sergio
authors.initials: S
authors.lastname: Roa
authors.forename: Kaichun
authors.initials: K
authors.lastname: Wei
authors.forename: Robert L
authors.initials: RL
authors.lastname: Eoff
authors.forename: Rani S
authors.initials: RS
authors.lastname: Sellers
authors.forename: Alan B
authors.initials: AB
authors.lastname: Clark
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Kunkel
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Scharff
authors.forename: Winfried
authors.initials: W
authors.lastname: Edelmann
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics; D000818:Animals; D059766:DNA End-Joining Repair / Q000235:genetics; D053843:DNA Mismatch Repair / Q000235:genetics; D045643:DNA Repair Enzymes / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D005090:Exodeoxyribonucleases / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D005260:Female; D008297:Male; D008540:Meiosis / Q000235:genetics; D051379:Mice; D057507:Mice, 129 Strain; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008817:Mice, Mutant Strains; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D050505:Mutant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
chemical_list: D050505:Mutant Proteins; C583623:Exo1 protein, mouse; D005090:Exodeoxyribonucleases; C028450:exodeoxyribonuclease I; D045643:DNA Repair Enzymes
keywords: scaffold function; somatic hypermuation; ssDNA