title: Nuclear localization of human DNA mismatch repair protein exonuclease 1 (hEXO1).
abstract: Human exonuclease 1 (hEXO1) is implicated in DNA mismatch repair (MMR) and mutations in hEXO1 may be associated with hereditary nonpolyposis colorectal cancer (HNPCC). Since the subcellular localization of MMR proteins is essential for proper MMR function, we characterized possible nuclear localization signals (NLSs) in hEXO1. Using fluorescent fusion proteins, we show that the sequence 418KRPR421, which exhibit strong homology to other monopartite NLS sequences, is responsible for correct nuclear localization of hEXO1. This NLS sequence is located in a region that is also required for hEXO1 interaction with hMLH1 and we show that defective nuclear localization of hEXO1 mutant proteins could be rescued by hMLH1 or hMSH2. Both hEXO1 and hMLH1 form complexes with the nuclear import factors importin beta/alpha1,3,7 whereas hMSH2 specifically recognizes importin beta/alpha3. Taken together, we infer that hEXO1, hMLH1 and hMSH2 form complexes and are imported to the nucleus together, and that redundant NLS import signals in the proteins may safeguard nuclear import and thereby MMR activity.
authors.affiliation: Department of Science, Systems and Models, Roskilde University, Denmark.
authors.forename: Nina Østergaard
authors.initials: NØ
authors.lastname: Knudsen
authors.forename: Finn Cilius
authors.initials: FC
authors.lastname: Nielsen
authors.forename: Lena
authors.initials: L
authors.lastname: Vinther
authors.forename: Ronni
authors.initials: R
authors.lastname: Bertelsen
authors.forename: Steen
authors.initials: S
authors.lastname: Holten-Andersen
authors.forename: Sascha Emilie
authors.initials: SE
authors.lastname: Liberti
authors.forename: Robert
authors.initials: R
authors.lastname: Hofstra
authors.forename: Krista
authors.initials: K
authors.lastname: Kooi
authors.forename: Lene Juel
authors.initials: LJ
authors.lastname: Rasmussen
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D002467:Cell Nucleus / Q000201:enzymology*; D053843:DNA Mismatch Repair; D045643:DNA Repair Enzymes / Q000032:analysis* / Q000235:genetics / Q000378:metabolism*; D005090:Exodeoxyribonucleases / Q000032:analysis* / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D028884:Karyopherins / Q000378:metabolism; D051379:Mice; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein / Q000378:metabolism; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D028884:Karyopherins; C501486:MLH1 protein, human; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins; C114331:EXO1 protein, human; D005090:Exodeoxyribonucleases; C497172:MSH2 protein, human; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein; D045643:DNA Repair Enzymes