title: Nuclear localization of the Saccharomyces cerevisiae ribonucleotide reductase small subunit requires a karyopherin and a WD40 repeat protein.
abstract: Ribonucleotide reductase (RNR) catalyzes the reduction of ribonucleotides to the corresponding deoxyribonucleotides and is an essential enzyme for DNA replication and repair. Cells have evolved intricate mechanisms to regulate RNR activity to ensure high fidelity of DNA replication during normal cell-cycle progression and of DNA repair upon genotoxic stress. The RNR holoenzyme is composed of a large subunit R1 (alpha, oligomeric state unknown) and a small subunit R2 (beta(2)). R1 binds substrates and allosteric effectors; R2 contains a diferric-tyrosyl radical [(Fe)(2)-Y.] cofactor that is required for catalysis. In Saccharomyces cerevisiae, R1 is predominantly localized in the cytoplasm, whereas R2, which is a heterodimer (betabeta'), is predominantly in the nucleus. When cells encounter DNA damage or stress during replication, betabeta' is redistributed from the nucleus to the cytoplasm in a checkpoint-dependent manner, resulting in the colocalization of R1 and R2. We have identified two proteins that have an important role in betabeta' nuclear localization: the importin beta homolog Kap122 and the WD40 repeat protein Wtm1. Deletion of either WTM1 or KAP122 leads to loss of betabeta' nuclear localization. Wtm1 and its paralog Wtm2 are both nuclear proteins that are in the same protein complex with betabeta'. Wtm1 also interacts with Kap122 in vivo and requires Kap122 for its nuclear localization. Our results suggest that Wtm1 acts either as an adaptor to facilitate nuclear import of betabeta' by Kap122 or as an anchor to retain betabeta' in the nucleus.
authors.affiliation: Department of Biochemistry and Molecular Genetics, University of Colorado Health Sciences Center, Aurora, CO 80045, USA.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Zhang
authors.forename: Xiuxiang
authors.initials: X
authors.lastname: An
authors.forename: Kui
authors.initials: K
authors.lastname: Yang
authors.forename: Deborah L
authors.initials: DL
authors.lastname: Perlstein
authors.forename: Leslie
authors.initials: L
authors.lastname: Hicks
authors.forename: Neil
authors.initials: N
authors.lastname: Kelleher
authors.forename: JoAnne
authors.initials: J
authors.lastname: Stubbe
authors.forename: Mingxia
authors.initials: M
authors.lastname: Huang
mesh_terms: D002384:Catalysis; D002467:Cell Nucleus / Q000201:enzymology* / Q000378:metabolism; D047369:Chromatin Immunoprecipitation; D003593:Cytoplasm / Q000378:metabolism; D004249:DNA Damage; D004261:DNA Replication; D019281:Dimerization; D004591:Electrophoresis, Polyacrylamide Gel; D005656:Fungal Proteins / Q000737:chemistry; D017353:Gene Deletion; D015966:Gene Expression Regulation, Fungal; D005800:Genes, Fungal; D049452:Green Fluorescent Proteins / Q000737:chemistry; D028884:Karyopherins / Q000378:metabolism / Q000502:physiology*; D008954:Models, Biological; D009154:Mutation; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D012097:Repressor Proteins / Q000737:chemistry / Q000502:physiology*; D012264:Ribonucleotide Reductases / Q000096:biosynthesis* / Q000737:chemistry; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D014157:Transcription Factors / Q000737:chemistry / Q000502:physiology*; D028961:beta Karyopherins / Q000378:metabolism / Q000502:physiology*
chemical_list: D005656:Fungal Proteins; C423162:KAP122 protein, S cerevisiae; D028884:Karyopherins; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; C107277:Wtm1 protein, S cerevisiae; C107278:Wtm2 protein, S cerevisiae; D028961:beta Karyopherins; D049452:Green Fluorescent Proteins; D012264:Ribonucleotide Reductases