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Abstract
The synthesis, processing and function of coding and non-coding RNA molecules and their interacting proteins has been the focus of a great deal of research that has boosted our understanding of key molecular pathways that underlie higher order events such as cell cycle control, development, innate immune response and the occurrence of genetic diseases. In this study, we have found that formamide preferentially weakens RNA related processes in vivo. Using a non-essential Schizosaccharomyces pombe gene deletion collection, we identify deleted loci that make cells sensitive to formamide. Sensitive deletions are significantly enriched in genes involved in RNA metabolism. Accordingly, we find that previously known temperature-sensitive splicing mutants become lethal in the presence of the drug under permissive temperature. Furthermore, in a wild type background, splicing efficiency is decreased and R-loop formation is increased in the presence of formamide. In addition, we have also isolated 35 formamide-sensitive mutants, many of which display remarkable morphology and cell cycle defects potentially unveiling new players in the regulation of these processes. We conclude that formamide preferentially targets RNA related processes in vivo, probably by relaxing RNA secondary structures and/or RNA-protein interactions, and can be used as an effective tool to characterize these processes.
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2
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Garcia V, Furuya K, Carr AM. Identification and functional analysis of TopBP1 and its homologs. DNA Repair (Amst) 2005; 4:1227-39. [PMID: 15897014 DOI: 10.1016/j.dnarep.2005.04.001] [Citation(s) in RCA: 137] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2005] [Revised: 04/11/2005] [Accepted: 04/11/2005] [Indexed: 01/18/2023]
Abstract
The multiple BRCT-domain protein TopBP1 and its yeast homologs have been implicated in many aspects of DNA metabolism, but their molecular functions remain elusive. In this review, we first summarise how the yeast homologs were identified and characterised. We next review the data available from metazoan systems and finally draw parallels with the yeast models. TopBP1 plays important functions in the initiation of DNA replication in all organisms and participates in checkpoint responses both within S phase and following DNA damage. In metazoan systems there is accumulating evidence for additional roles in transcriptional regulation that have not been reported in yeast. Overall, TopBP1 appears to play a key role in integrating different aspects of DNA metabolism, but the mechanistic basis for this remains to be fully explained.
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Affiliation(s)
- Valerie Garcia
- Genome Damage and Stability Center, University of Sussex, Brighton, Sussex BN1 9RQ, UK
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3
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Asaad NA, Zeng ZC, Guan J, Thacker J, Iliakis G. Homologous recombination as a potential target for caffeine radiosensitization in mammalian cells: reduced caffeine radiosensitization in XRCC2 and XRCC3 mutants. Oncogene 2000; 19:5788-800. [PMID: 11126366 DOI: 10.1038/sj.onc.1203953] [Citation(s) in RCA: 83] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The radiosensitizing effect of caffeine has been associated with the disruption of multiple DNA damage-responsive cell cycle checkpoints, but several lines of evidence also implicate inhibition of DNA repair. The role of DNA repair inhibition in caffeine radiosensitization remains uncharacterized, and it is unknown which repair process, or lesion, is affected. We show that a radiosensitive cell line, mutant for the RAD51 homolog XRCC2 and defective in homologous recombination repair (HRR), displays significantly diminished caffeine radiosensitization that can be restored by expression of XRCC2. Despite the reduced radiosensitization, caffeine effectively abrogates checkpoints in S and G2 phases in XRCC2 mutant cells indicating that checkpoint abrogation is not sufficient for radiosensitization. Another radiosensitive line, mutant for XRCC3 and defective in HRR, similarly shows reduced caffeine radiosensitization. On the other hand, a radiosensitive mutant (irs-20) of DNA-PKcs with a defect in non-homologous end-joining (NHEJ) is radiosensitized by caffeine to an extent comparable to wild-type cells. In addition, rejoining of radiation-induced DNA DSBs, that mainly reflects NHEJ, remains unaffected by caffeine in XRCC2 and XRCC3 mutants, or their wild-type counterparts. These observations suggest that caffeine targets steps in HRR but not in NHEJ and that abrogation of checkpoint response is not sufficient to explain radiosensitization. Indeed, immortalized fibroblasts from AT patients show caffeine radiosensitization despite the checkpoint defects associated with ATM mutation. We propose that caffeine radiosensitization is mediated by inhibition of stages in DNA DSB repair requiring HRR and that checkpoint disruption contributes by allowing these DSBs to transit into irreparable states. Thus, checkpoints may contribute to genomic stability by promoting error-free HRR.
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Affiliation(s)
- N A Asaad
- Department of Radiation Oncology of Kimmel Cancer Center, Jefferson Medical College, Philadelphia, Pennsylvania 19107, USA
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4
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Abstract
This review is concerned with repair and tolerance of UV damage in the fission yeast, Schizosaccharomyces pombe and with the differences between Sch. pombe and budding yeast, Saccharomyces cerevisiae in their response to UV irradiation. Sch. pombe is not as sensitive to ultra-violet radiation as Sac. cerevisiae nor are any of its mutants as sensitive as the most sensitive Sac. cerevisiae mutants. This can be explained in part by the fact that Sch. pombe, unlike budding yeast or mammalian cells, has an extra pathway (UVER) for excision of UV photoproducts in addition to nucleotide excision repair (NER). However, even in mutants lacking this additional pathway, there are significant differences between the two yeasts. Sch. pombe mutants that lack the alternative pathway are still more UV-resistant than wild-type Sac. cerevisiae; recombination mutants are significantly UV sensitive (unlike their Sac. cerevisiae equivalents); mutants lacking the second pathway are sensitized to UV by caffeine; and checkpoint mutants are relatively more sensitive than the budding yeast equivalents. In addition, Sch. pombe has no photolyase. Thus, the response to UV in the two yeasts has a number of significant differences, which are not accounted for entirely by the existence of two alternative excision repair pathways. The long G2 in Sch. pombe, its well-developed recombination pathways and efficient cell cycle checkpoints are all significant components in survival of UV damage.
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Affiliation(s)
- S J McCready
- Department of Biochemistry, University of Oxford, South Parks Road, OX1 3QU, Oxford, UK.
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5
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Hofmann AF, Harris SD. The Aspergillus nidulans uvsB gene encodes an ATM-related kinase required for multiple facets of the DNA damage response. Genetics 2000; 154:1577-86. [PMID: 10747054 PMCID: PMC1461047 DOI: 10.1093/genetics/154.4.1577] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
In Aspergillus nidulans, uvsB and uvsD belong to the same epistasis group of DNA repair mutants. Recent observations suggest that these genes are likely to control cell cycle checkpoint responses to DNA damage and incomplete replication. Consistent with this notion, we show here that UVSB is a member of the conserved family of ATM-related kinases. Phenotypic characterization of uvsB mutants shows that they possess defects in additional aspects of the DNA damage response besides checkpoint control, including inhibition of septum formation, regulation of gene expression, and induced mutagenesis. The musN227 mutation partially suppresses the poor growth and DNA damage sensitivity of uvsB mutants. Although musN227 partially suppresses several uvsB defects, it does not restore checkpoint function to uvsB mutants. Notably, the failure of uvsB mutants to restrain septum formation in the presence of DNA damage is suppressed by the musN227 mutation. We propose that UVSB functions as the central regulator of the A. nidulans DNA damage response, whereas MUSN promotes recovery by modulating a subset of the response.
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Affiliation(s)
- A F Hofmann
- Department of Microbiology, University of Connecticut Health Center, Farmington, Connecticut 06030-3205, USA
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6
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Lieberman HB, Hopkins KM. Schizosaccharomyces malidevorans and Sz. octosporus homologues of Sz. pombe rad9, a gene that mediates radioresistance and cell-cycle progression. Gene 1994; 150:281-6. [PMID: 7821792 DOI: 10.1016/0378-1119(94)90438-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The rad9 gene of Schizosaccharomyces pombe is involved in promoting resistance to ionizing radiation and UV light, as well as regulating cell cycle progression after irradiation. We have isolated functional rad9 cognates from two other fission yeasts, Sz. malidevorans and Sz. octosporus, that can restore radioresistance and the radiation-induced G2 delay response to Sz. pombe rad9::ura4 cells. The Sz. pombe and Sz. malidevorans genes are identical at the nucleotide sequence level, which reflects their close evolutionary relationship. Each bears three introns and codes for a 47 464-Da protein that contain 426 amino acids (aa). In contrast, Sz. octosporus rad9 contains five introns and codes for a 48 210-Da protein that is 432-aa long. The Sz. pombe rad9 product is only 65% identical and 80% similar to the corresponding Sz. octosporus gene product. All of the strains synthesize a rad9 RNA of approx. 1.6 kb. The presence of a rad9-like gene in these yeasts suggests that the cellular process(es) mediated by rad9, and used by these organisms to increase survival and transiently delay cycling in G2 after irradiation, are conserved. The isolation, analyses and comparison of rad9 genes from different organisms should aid in elucidating the specific biological role of the corresponding protein and especially help pinpoint regions important for function.
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Affiliation(s)
- H B Lieberman
- Center for Radiological Research, Columbia University, New York, NY 10032
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7
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Zhao Y, Goriparthi L, Lieberman HB. A new shuttle vector system for the identification of spontaneous and radiation-induced mutations in the fission yeast Schizosaccharomyces pombe. Mutat Res 1994; 311:111-23. [PMID: 7526164 DOI: 10.1016/0027-5107(94)90079-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
A shuttle vector, pCRR1, has been constructed for the detection of spontaneous and radiation-induced mutations in the fission yeast Schizosaccharomyces pombe. This vector contains an Escherichia coli supF suppressor tRNA gene as the target for mutagenesis and bacterial pMB1 and yeast ars1 replication origins, which can be used to propagate the plasmid in bacterial and fission yeast cells, respectively. supF mutations can be detected after plasmid transformation into S. pombe and recovery in a bacterial indicator system, KS40/pKY241, by selecting for nalidixic acid resistance and/or by screening for lacZ- cells. We found that UV light or gamma-rays induced mutations in a dose-dependent manner in this system. Treatment of ultraviolet light (UV)-irradiated DNA with E. coli photolyase, which monomerizes cyclobutane pyrimidine dimers, before introduction into S. pombe reduced mutation frequencies to nearly background levels, indicating that this type of lesion is the major source of mutations. Comparison of spontaneous and UV-induced mutation frequencies in rad+, rad8-190 and rad13-A cells revealed no significant difference in background levels or induced levels after exposure to 100 J/m2 of UV. However, when plasmid DNA was UV-irradiated with 500 J/m2, the rad8-190 cells generated only 38% as many induced supF mutations as the rad+ strain, whereas the rad13-A cells produced more than a 6-fold increase in mutability relative to the level observed for the wild-type strain. These mutability patterns are consistent with previous studies that characterized rad8-190 cells as hypomutable and rad13-A cells as hypermutable by UV light at chromosomal loci. Thus, this shuttle vector system provides a useful and sensitive tool to assess mutability in S. pombe.
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Affiliation(s)
- Y Zhao
- Department of Radiation Oncology, College of Physicians and Surgeons, Columbia University, New York, NY 10032
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8
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Nasim A, Hannan MA. Cellular recovery, DNA repair and mutagenesis--a tale of two yeasts. Mutat Res 1993; 289:55-60. [PMID: 7689163 DOI: 10.1016/0027-5107(93)90130-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
In studies related to recovery and repair mechanisms following DNA damage, one problem that has been frequently addressed concerns the effects of DNA repair on both spontaneous and induced mutagenesis. Among the eukaryotic organisms which served as unique and valuable systems for investigating this problem are the two yeasts, Saccharomyces cerevisiae and Schizosaccharomyces pombe. With the basic genetics well worked out in both, these yeasts have provided the experimental tools for comparative analysis of mechanisms of DNA repair which show a great deal of diversity between the two unicellular eukaryotes. Since the present issue focuses on the contributions of R.H. Haynes to the area of DNA repair and mutagenesis, we have chosen to discuss those specific aspects of our studies which are directly or indirectly related to or influenced by his research in this field. These include: (i) liquid holding recovery, (ii) production of two strand mutations and the concept of heteroduplex repair, and (iii) understanding of pathways of repair through construction of supersensitive mutants in yeast.
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Affiliation(s)
- A Nasim
- Department of Biological and Medical Research, King Faisal Specialist Hospital and Research Centre, Riyadh, Saudi Arabia
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9
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Birkenbihl RP, Subramani S. Cloning and characterization of rad21 an essential gene of Schizosaccharomyces pombe involved in DNA double-strand-break repair. Nucleic Acids Res 1992; 20:6605-11. [PMID: 1480481 PMCID: PMC334577 DOI: 10.1093/nar/20.24.6605] [Citation(s) in RCA: 206] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Analysis of the Schizosaccharomyces pombe chromosomes by pulsed field gel electrophoresis showed that the fission yeast has a very efficient DNA double-strand-break (dsb) repair system, which properly restores the three chromosomes after they are degraded by gamma-irradiation. The radiation-sensitive mutant rad21-45 is deficient in this repair pathway but is capable of cell-cycle arrest in G2 following DNA damage. We cloned the rad21 gene by complementing the radiation sensitivity of the rad21-45 mutant. The plasmid-borne gene completely reestablished the DNA dsb repair pathway. The rad21 gene was localized to chromosome III by hybridization. The transcript is 2.5 kb long and expressed at a moderate level. The 1884-bp open reading frame encodes a 628 amino acid, very acidic peptide with a calculated molecular mass of 67,854 D. The rad21 gene shows no significant homology to other known nucleotide or peptide sequences. The inability of the mutant to perform efficient DNA repair is caused by a single base substitution, which changes wild-type isoleucine67 into threonine in the mutant. Deletion of the genomic rad21 gene showed that it is essential for mitotic growth of S.pombe.
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Affiliation(s)
- R P Birkenbihl
- Department of Biology, University of California, San Diego, La Jolla 92093-0322
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10
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Seaton BL, Yucel J, Sunnerhagen P, Subramani S. Isolation and characterization of the Schizosaccharomyces pombe rad3 gene, involved in the DNA damage and DNA synthesis checkpoints. Gene 1992; 119:83-9. [PMID: 1398093 DOI: 10.1016/0378-1119(92)90069-2] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
We have cloned the Schizosaccharomyces pombe rad3 gene which is involved in G2 arrest following DNA damage, and in the dependence of mitosis on the completion of DNA replication. The gene was cloned by complementation of the sensitivity to UV light and gamma rays of the rad3-136 mutant with an Sz. pombe genomic library. Sublocalization of the complementing activity and sequencing of the clone identified an intronless 3210-bp open reading frame capable of encoding a 1070-amino acid protein with an M(r) of 121974. The rad3 gene is a new gene with no homologs in existing sequence databases. The gene is poorly expressed, with a codon bias index of -0.01. A disruption mutant affecting the coding region was only slightly more sensitive to UV light than the original rad3-136 mutant. The rad3 gene was mapped to NotI fragment C on chromosome II.
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Affiliation(s)
- B L Seaton
- Department of Biology, University of California, San Diego La Jolla 92093-0322
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11
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Lieberman HB, Hopkins KM, Laverty M, Chu HM. Molecular cloning and analysis of Schizosaccharomyces pombe rad9, a gene involved in DNA repair and mutagenesis. MOLECULAR & GENERAL GENETICS : MGG 1992; 232:367-76. [PMID: 1588907 DOI: 10.1007/bf00266239] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The mutant allele rad9-192 renders Schizosaccharomyces pombe cells sensitive to ionizing radiation and UV light. We have isolated from a S. pombe genomic DNA library a unique recombinant plasmid that is capable of restoring wild-type levels of radioresistance to a rad9-192-containing cell population. Plasmid integration studies using the cloned DNA, coupled with mating and tetrad analyses, indicate that this isolated DNA contains the wild-type rad9 gene. We inactivated the repair function of the cloned fragment by a single insertion of the S. pombe ura4 gene. This nonfunctional fragment was used to create a viable disruption mutant, thus demonstrating that the rad9 gene does not encode an essential cellular function. In addition, the rad9-192 mutant population is as radiosensitive as the disruption mutant, indicating that rad9 gene function is severely if not totally inhibited by the molecular defect responsible for the rad9-192 phenotype. DNA sequence analysis of rad9 reveals an open reading frame of 1,278 bp, interrupted by three introns 53 bp, 57 bp, and 56 bp long, respectively, and ending in the termination codon TAG. This gene is capable of encoding a protein of 426 amino acids, with a corresponding calculated molecular weight of 47,464 daltons. No significant homology was detected between the rad9 gene or its deduced protein sequence and sequences previously entered into DNA and protein sequence data banks.
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Affiliation(s)
- H B Lieberman
- Department of Radiation Oncology, Columbia University College of Physicians and Surgeons, New York, NY 10032
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12
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Fenech M, Carr AM, Murray J, Watts FZ, Lehmann AR. Cloning and characterization of the rad4 gene of Schizosaccharomyces pombe; a gene showing short regions of sequence similarity to the human XRCC1 gene. Nucleic Acids Res 1991; 19:6737-41. [PMID: 1762905 PMCID: PMC329303 DOI: 10.1093/nar/19.24.6737] [Citation(s) in RCA: 61] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The rad4.116 mutant of the fission yeast Schizosaccharomyces pombe is temperature-sensitive for growth, as well as being sensitive to the killing actions of both ultraviolet light and ionizing radiation. We have cloned the rad4 gene by complementation of the temperature sensitive phenotype of the rad4.116 mutant with a S. pombe gene bank. The rad4 gene fully complemented the UV sensitivity of the rad4.116 mutant. The gene is predicted to encode a protein of 579 amino acids with a basic tail, a possible zinc finger and a nuclear location signal. The amino terminal part of the predicted rad4 ORF contains two short regions of similarity to the C-terminal part of the human XRCC1 gene. Codon usage suggests that the gene is very poorly expressed, and this was confirmed by RNA studies. Gene disruption showed that the rad4 gene was essential for the mitotic growth of S. pombe.
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Affiliation(s)
- M Fenech
- MRC Cell Mutation Unit, School of Biology, University of Sussex, Falmer, Brighton, UK
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13
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Abstract
The fission yeast Schizosaccharomyces pombe serves as an excellent alternative and complementary model system for the analysis of genes and gene products involved in DNA repair. This brief review outlines the advantages of S. pombe and describes the radiation-sensitive mutants available for the analysis of DNA repair and recombination mechanisms in this organism. The progress in the cloning and characterization of representative genes is also described.
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Affiliation(s)
- S Subramani
- Department of Biology, University of California, San Diego, La Jolla 92093
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14
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Abstract
Mutants of the fission yeast Schizosaccharomyces pombe which are sensitive to UV and/or gamma-irradiation have been assigned to 23 complementation groups, which can be assigned to three phenotypic groups. We have cloned genes which correct the deficiency in mutants corresponding to 12 of the complementation groups. Three genes in the excision-repair pathway have a high degree of sequence conservation with excision-repair genes from the evolutionarily distant budding yeast Saccharomyces cerevisiae. In contrast, those genes in the recombination repair pathway which have been characterised so far, show little homology with any previously characterised genes.
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Affiliation(s)
- A R Lehmann
- MRC Cell Mutation Unit, School of Biology, Sussex University, Falmer, Brighton, Great Britain
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15
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Cloning and analysis of a gene involved in DNA repair and recombination, the rad1 gene of Schizosaccharomyces pombe. Mol Cell Biol 1990. [PMID: 2355921 DOI: 10.1128/mcb.10.7.3750] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We have cloned the rad1 gene of Schizosaccharomyces pombe by complementation of the rad1-1 mutant, which is deficient in DNA repair and recombination. The coding region of the gene is 582 base pairs long and contains no introns. The predicted product is a strongly acidic, 22-kilodalton protein containing 194 amino acid residues. This gene does not exhibit significant homology to any other known repair gene. The major transcription start site is at 27 base pairs upstream of the putative start codon. Insertion mutagenesis revealed that besides the coding region, at least 151 base pairs of 5'-flanking sequence are required for full complementing activity. A strain carrying a null allele of rad1 was constructed and found to have a phenotype closely similar to that of the rad1-1 mutant. Expression in Escherichia coli of the coding region yielded a protein product of a size close to that predicted from the DNA sequence. This product reacted with antibodies raised against a synthetic peptide with a sequence from that predicted for the protein product. We have localized the rad1 gene to NotI fragment E of the S. pombe genome.
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16
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Benk� Z, Sipiczki M. Caffeine-resistance in Schizosaccharomyces pombe: a pleiotropic mutation affecting UV-sensitivity, fertility, and cell cycle. Curr Genet 1990. [DOI: 10.1007/bf00321114] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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17
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Sunnerhagen P, Seaton BL, Nasim A, Subramani S. Cloning and analysis of a gene involved in DNA repair and recombination, the rad1 gene of Schizosaccharomyces pombe. Mol Cell Biol 1990; 10:3750-60. [PMID: 2355921 PMCID: PMC360827 DOI: 10.1128/mcb.10.7.3750-3760.1990] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
We have cloned the rad1 gene of Schizosaccharomyces pombe by complementation of the rad1-1 mutant, which is deficient in DNA repair and recombination. The coding region of the gene is 582 base pairs long and contains no introns. The predicted product is a strongly acidic, 22-kilodalton protein containing 194 amino acid residues. This gene does not exhibit significant homology to any other known repair gene. The major transcription start site is at 27 base pairs upstream of the putative start codon. Insertion mutagenesis revealed that besides the coding region, at least 151 base pairs of 5'-flanking sequence are required for full complementing activity. A strain carrying a null allele of rad1 was constructed and found to have a phenotype closely similar to that of the rad1-1 mutant. Expression in Escherichia coli of the coding region yielded a protein product of a size close to that predicted from the DNA sequence. This product reacted with antibodies raised against a synthetic peptide with a sequence from that predicted for the protein product. We have localized the rad1 gene to NotI fragment E of the S. pombe genome.
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Affiliation(s)
- P Sunnerhagen
- Department of Biology B-022, University of California, San Diego, La Jolla 92093
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18
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Abstract
Traditionally, sexual reproduction has been explained as an adaptation for producing genetic variation through allelic recombination. Serious difficulties with this explanation have led many workers to conclude that the benefit of sex is a major unsolved problem in evolutionary biology. A recent informational approach to this problem has led to the view that the two fundamental aspects of sex, recombination and outcrossing, are adaptive responses to the two major sources of noise in transmitting genetic information, DNA damage and replication errors. We refer to this view as the repair hypothesis, to distinguish it from the traditional variation hypothesis. On the repair hypothesis, recombination is a process for repairing damaged DNA. In dealing with damage, recombination produces a form of informational noise, allelic recombination, as a by-product. Recombinational repair is the only repair process known which can overcome double-strand damages in DNA, and such damages are common in nature. Recombinational repair is prevalent from the simplest to the most complex organisms. It is effective against many different types of DNA-damaging agents, and, in particular, is highly efficient in overcoming double-strand damages. Current understanding of the mechanisms of recombination during meiosis suggests that meiosis is designed for repairing DNA. These considerations form the basis for the first part of the repair hypothesis, that recombination is an adaptation for dealing with DNA damage. The evolution of sex can be viewed as a continuum on the repair hypothesis. Sex is presumed to have arisen in primitive RNA-containing protocells whose sexual process was similar to that of recombinational repair in extent segmented, single-stranded RNA viruses, which are among the simplest known organisms. Although this early form of repair occurred by nonenzymatic reassortment of replicas of undamaged RNA segments, it evolved into enzyme-mediated breakage and exchange between long DNA molecules. As some lines of descent became more complex, their genome information increased, leading to increased vulnerability to mutation. The diploid stage of the sexual cycle, which was at first transient, became the predominant stage in some lines of descent because it allowed complementation, the masking of deleterious recessive mutations. Out-crossing, the second fundamental aspect of sex, is also maintained by the advantage of masking mutations. However, outcrossing can be abandoned in favor of parthenogenesis or selfing under conditions in which the costs of mating are very high.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- H Bernstein
- Department of Microbiology and Immunology, College of Medicine, University of Arizona, Tucson 85724
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19
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Phipps J, Nasim A, Miller DR. Recovery, repair, and mutagenesis in Schizosaccharomyces pombe. ADVANCES IN GENETICS 1985; 23:1-72. [PMID: 3887858 DOI: 10.1016/s0065-2660(08)60511-8] [Citation(s) in RCA: 97] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
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20
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Grossenbacher-Grunder AM, Thuriaux P. Spontaneous and UV-induced recombination in radiation-sensitive mutants of Schizosaccharomyces pombe. Mutat Res 1981; 81:37-48. [PMID: 7254221 DOI: 10.1016/0027-5107(81)90085-3] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
The rad alleles of 18 unlinked genes of S. pombe were tested for their level of spontaneous meiotic, spontaneous mitotic and UV-induced mitotic recombination in the ade7-50 x ade7-152 interval. The effects of these rad alleles on meiosis and cell morphology were also studied. None of these mutants showed a clear-cut reduction of spontaneous recombination rates, no matter whether they had lost or retained a caffeine-sensitive repair of UV-induced lesions, which has previously been interpreted as a recombinational pathway of DNA repair (Fabre, 1972a; Gentner, 1977; Gentner et al., 1978). rad1-1 was the only mutant with a reduced frequency of UV-induced recombination. Some mutants displayed an increased frequency of mitotic recombination, either spontaneously (rad 15-P, rad 21-45), UV-induced (rad8-190) or both (rad2-44). Previous hypothesis on the contribution of recombination to DNA repair in S. pombe are reconsidered in the light of these data.
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21
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Gentner NE. Both caffeine-induced lethality and the negative liquid holding effect, in UV- or gamma-irradiated wild-type Schizosaccharomyces pombe, are consequences of interference with a recombinational repair process. MOLECULAR & GENERAL GENETICS : MGG 1981; 181:283-7. [PMID: 6941064 DOI: 10.1007/bf00425598] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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22
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Hoetzer KE, Deering RA. Sensitization of rad mutants of Dictyostelium discoideum to ultraviolet light by postirradiation treatment with caffeine. Mutat Res 1980; 71:273-6. [PMID: 6248778 DOI: 10.1016/0027-5107(80)90080-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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Rosen H, Rehn MM, Johnson BA. The effect of caffeine on repair in Chlamydomonas reinhardtii. I. Enhancement of recombination repair. Mutat Res 1980; 70:301-9. [PMID: 7383037 DOI: 10.1016/0027-5107(80)90020-2] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The effect of caffeine on repair was studied in the green alga Chlamydomonas reinhardtii. Treatment of UV-irradiated wild-type (UVS+) cells with a sublethal level of caffeine caused a significant increase in survival compared to untreated UV-irradiated cells. Caffeine did not affect survival in the repair-deficient strain UVSE1, which is deficient in repair of UV-induced damage carried out by enzymes associated with recombination during meiosis. A significant increase in survival in the presence of caffeine was observed in the repair-deficient strain UVSE4 in which recombination during meiosis is not affected. Treatment of zygotes homozygous for UVS+, UVSE1, or UVSE4 with sublethal levels of caffeine caused marked increases in recombination frequency in UVS+ and UVSE4 zygotes and no increase in recombination in UVSE1 zygotes. These results indicate that caffeine increases recombination in normal strains. Increased opportunity for recombination caused by caffeine would not result in increased recombination frequency in the UVSE1 strain, assuming limited-recombination enzyme activity in this strain. The observed increase in survival following UV-irradiation in the presence of caffeine in strains having normal recombination would therefore be associated with a caffeine-induced increase in opportunities for recombination repair.
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Abstract
Four caffeine-resistant haploid isolates, two resistant to 50 mM caffeine and two resistant to 100 mM caffeine, were genetically analyzed. Complementation and tetrad analysis indicated that all four mutations are alleles of the same locus. All four isolates demonstrated incomplete dominance when hybridized to the wild-type strain and dominance of high to low resistance when hybridized to one another. Differences in caffeine resistance were found between wild-type grande cells and its petite derivative.
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