title: Characterization of Saccharomyces cerevisiae dna2 mutants suggests a role for the helicase late in S phase.
abstract: The TOR proteins, originally identified as targets of the immunosuppressant rapamycin, contain an ATM-like "lipid kinase" domain and are required for early G1 progression in eukaryotes. Using a screen to identify Saccharomyces cerevisiae mutants requiring overexpression of Tor1p for viability, we have isolated mutations in a gene we call ROT1 (requires overexpression of Tor1p). This gene is identical to DNA2, encoding a helicase required for DNA replication. As with its role in cell cycle progression, both the N-terminal and C-terminal regions, as well as the kinase domain of Tor1p, are required for rescue of dna2 mutants. Dna2 mutants are also rescued by Tor2p and show synthetic lethality with tor1 deletion mutants under specific conditions. Temperature-sensitive (Ts) dna2 mutants arrest irreversibly at G2/M in a RAD9- and MEC1-dependent manner, suggesting that Dna2p has a role in S phase. Frequencies of mitotic recombination and chromosome loss are elevated in dna2 mutants, also supporting a role for the protein in DNA synthesis. Temperature-shift experiments indicate that Dna2p functions during late S phase, although dna2 mutants are not deficient in bulk DNA synthesis. These data suggest that Dna2p is not required for replication fork progression but may be needed for a later event such as Okazaki fragment maturation.
authors.affiliation: Department of Developmental Biology, Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, California 94305, USA.
authors.forename: D F
authors.initials: DF
authors.lastname: Fiorentino
authors.forename: G R
authors.initials: GR
authors.lastname: Crabtree
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D003001:Cloning, Molecular; D004265:DNA Helicases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004261:DNA Replication / Q000235:genetics*; D004271:DNA, Fungal / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D020043:Genes, Essential / Q000235:genetics; D005800:Genes, Fungal / Q000235:genetics / Q000502:physiology; D016153:Genes, Suppressor / Q000235:genetics; D047908:Intracellular Signaling Peptides and Proteins; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics*; D010641:Phenotype; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases; D011995:Recombination, Genetic / Q000235:genetics; D016196:S Phase / Q000235:genetics*; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000201:enzymology* / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins; D017384:Sequence Deletion / Q000235:genetics; D013696:Temperature
chemical_list: D000251:Adenosine Triphosphatases; D018797:Cell Cycle Proteins; D004265:DNA Helicases; D004271:DNA, Fungal; D005656:Fungal Proteins; D047908:Intracellular Signaling Peptides and Proteins; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D017346:Protein Serine-Threonine Kinases; D029701:Saccharomyces cerevisiae Proteins; C069930:rad9 protein; C083324:TOR1 protein, S cerevisiae; C081135:TOR2 protein, S cerevisiae; C088937:MEC1 protein, S cerevisiae; C410222:DNA2 protein, S cerevisiae