Cis-Elements Governing Trinucleotide Repeat Instability in Saccharomyces cerevisiae

Abstract Trinucleotide repeat (TNR) instability in humans is governed by unique cis-elements. One element is a threshold, or minimal repeat length, conferring frequent mutations. Since thresholds have not been directly demonstrated in model systems, their molecular nature remains uncertain. Another element is sequence specificity. Unstable TNR sequences are almost always CNG, whose hairpin-forming ability is thought to promote instability by inhibiting DNA repair. To understand these cis-elements further, TNR expansions and contractions were monitored by yeast genetic assays. A threshold of ∼15–17 repeats was observed for CTG expansions and contractions, indicating that thresholds function in organisms besides humans. Mutants lacking the flap endonuclease Rad27p showed little change in the expansion threshold, suggesting that this element is not altered by the presence or absence of flap processing. CNG or GNC sequences yielded frequent mutations, whereas A-T rich sequences were substantially more stable. This sequence analysis further supports a hairpin-mediated mechanism of TNR instability. Expansions and contractions occurred at comparable rates for CTG tract lengths between 15 and 25 repeats, indicating that expansions can comprise a significant fraction of mutations in yeast. These results indicate that several unique cis-elements of human TNR instability are functional in yeast.

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Stabilizing Effects of Interruptions on Trinucleotide Repeat Expansions in Saccharomyces cerevisiae

Molecular and Cellular Biology ◽

10.1128/mcb.20.1.173-180.2000 ◽

2000 ◽

Vol 20 (1) ◽

pp. 173-180 ◽

Cited By ~ 39

Author(s):

Michael L. Rolfsmeier ◽

Robert S. Lahue

Keyword(s):

Saccharomyces Cerevisiae ◽

Base Pair ◽

Trinucleotide Repeat ◽

Primary Factor ◽

Yeast Cells ◽

Repeat Expansions ◽

Yeast Genetic ◽

Hairpin Formation ◽

Lagging Strand ◽

Genetic Assay

ABSTRACT In most trinucleotide repeat (TNR) diseases, the primary factor determining the likelihood of expansions is the length of the TNR. In some diseases, however, stable alleles contain one to three base pair substitutions that interrupt the TNR tract. The unexpected stability of these alleles compared to the frequent expansions of perfect TNRs suggested that interruptions somehow block expansions and that expansions occur only upon loss of at least one interruption. The work in this study uses a yeast genetic assay to examine the mechanism of stabilization conferred by two interruptions of a 25-repeat tract. Expansion rates are reduced up to 90-fold compared to an uninterrupted allele. Stabilization is greatest when the interruption is replicated early on the lagging strand, relative to the rest of the TNR. Although expansions are infrequent, they are often polar, gaining new DNA within the largest available stretch of perfect repeats. Surprisingly, interruptions are always retained and sometimes even duplicated, suggesting that expansion in yeast cells can proceed without loss of the interruption. These findings support a stabilization model in which interruptions contribute in cis to reduce hairpin formation during TNR replication and thus inhibit expansion rates.

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The SRS2 suppressor of rad6 mutations of Saccharomyces cerevisiae acts by channeling DNA lesions into the RAD52 DNA repair pathway.

Genetics ◽

10.1093/genetics/124.4.817 ◽

1990 ◽

Vol 124 (4) ◽

pp. 817-831 ◽

Cited By ~ 6

Author(s):

R H Schiestl ◽

S Prakash ◽

L Prakash

Keyword(s):

Saccharomyces Cerevisiae ◽

Dna Repair ◽

Gamma Ray ◽

Dna Lesions ◽

Recombinational Repair ◽

Repair Pathway ◽

Uv Mutagenesis ◽

Uv Sensitivity ◽

Suppressor Mutations ◽

Induced Mutagenesis

Abstract rad6 mutants of Saccharomyces cerevisiae are defective in the repair of damaged DNA, DNA damage induced mutagenesis, and sporulation. In order to identify genes that can substitute for RAD6 function, we have isolated genomic suppressors of the UV sensitivity of rad6 deletion (rad6 delta) mutations and show that they also suppress the gamma-ray sensitivity but not the UV mutagenesis or sporulation defects of rad6. The suppressors show semidominance for suppression of UV sensitivity and dominance for suppression of gamma-ray sensitivity. The six suppressor mutations we isolated are all alleles of the same locus and are also allelic to a previously described suppressor of the rad6-1 nonsense mutation, SRS2. We show that suppression of rad6 delta is dependent on the RAD52 recombinational repair pathway since suppression is not observed in the rad6 delta SRS2 strain containing an additional mutation in either the RAD51, RAD52, RAD54, RAD55 or RAD57 genes. Possible mechanisms by which SRS2 may channel unrepaired DNA lesions into the RAD52 DNA repair pathway are discussed.

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Crosstalk between Different DNA Repair Pathways Contributes to Neurodegenerative Diseases

Biology ◽

10.3390/biology10020163 ◽

2021 ◽

Vol 10 (2) ◽

pp. 163

Author(s):

Swapnil Gupta ◽

Panpan You ◽

Tanima SenGupta ◽

Hilde Nilsen ◽

Kulbhushan Sharma

Keyword(s):

Dna Repair ◽

Neurodegenerative Diseases ◽

3D Models ◽

Model Systems ◽

Spinocerebellar Ataxias ◽

C Elegans ◽

Cellular Processes ◽

Age Related ◽

Damage Response ◽

Lateral Sclerosis

Genomic integrity is maintained by DNA repair and the DNA damage response (DDR). Defects in certain DNA repair genes give rise to many rare progressive neurodegenerative diseases (NDDs), such as ocular motor ataxia, Huntington disease (HD), and spinocerebellar ataxias (SCA). Dysregulation or dysfunction of DDR is also proposed to contribute to more common NDDs, such as Parkinson’s disease (PD), Alzheimer’s disease (AD), and Amyotrophic Lateral Sclerosis (ALS). Here, we present mechanisms that link DDR with neurodegeneration in rare NDDs caused by defects in the DDR and discuss the relevance for more common age-related neurodegenerative diseases. Moreover, we highlight recent insight into the crosstalk between the DDR and other cellular processes known to be disturbed during NDDs. We compare the strengths and limitations of established model systems to model human NDDs, ranging from C. elegans and mouse models towards advanced stem cell-based 3D models.

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Metalloenzymes in DNA repair. Escherichia coli endonuclease IV and Saccharomyces cerevisiae Apn1.

Journal of Biological Chemistry ◽

10.1016/s0021-9258(18)54438-0 ◽

1991 ◽

Vol 266 (34) ◽

pp. 22893-22898

Author(s):

J.D. Levin ◽

R. Shapiro ◽

B. Demple

Keyword(s):

Escherichia Coli ◽

Saccharomyces Cerevisiae ◽

Dna Repair

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The Large Subunit of Replication Factor C (Rfclp/Cdc44p) Is Required for DNA Replication and DNA Repair in Saccharomyces cerevisiae

Genetics ◽

10.1093/genetics/142.1.65 ◽

1996 ◽

Vol 142 (1) ◽

pp. 65-78 ◽

Cited By ~ 7

Author(s):

Michael A McAlear ◽

K Michelle Tuffo ◽

Connie Holm

Keyword(s):

Saccharomyces Cerevisiae ◽

Dna Repair ◽

Dna Replication ◽

Uv Radiation ◽

Large Subunit ◽

Restrictive Temperature ◽

Replication Factor C ◽

Replication Factor ◽

Factor C

We used genetic and biochemical techniques to characterize the phenotypes associated with mutations affecting the large subunit of replication factor C (Cdc44p or Rfc1p) in Saccharomyces cerevisiae. We demonstrate that Cdc44p is required for both DNA replication and DNA repair in vivo. Cold-sensitive cdc44 mutants experience a delay in traversing S phase at the restrictive temperature following alpha factor arrest; although mutant cells eventually accumulate with a G2/M DNA content, they undergo a cell cycle arrest and initiate neither mitosis nor a new round of DNA synthesis. cdc44 mutants also exhibit an elevated level of spontaneous mutation, and they are sensitive both to the DNA damaging agent methylmethane sulfonate and to exposure to UV radiation. After exposure to UV radiation, cdc44 mutants at the restrictive temperature contain higher levels of single-stranded DNA breaks than do wild-type cells. This observation is consistent with the hypothesis that Cdc44p is involved in repairing gaps in the DNA after the excision of damaged bases. Thus, Cdc44p plays an important role in both DNA replication and DNA repair in vivo.

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The Schizosaccharomyces pombe cho1+ Gene Encodes a Phospholipid Methyltransferase

Genetics ◽

10.1093/genetics/150.2.553 ◽

1998 ◽

Vol 150 (2) ◽

pp. 553-562

Author(s):

Margaret I Kanipes ◽

John E Hill ◽

Susan A Henry

Keyword(s):

Saccharomyces Cerevisiae ◽

Sequence Analysis ◽

Schizosaccharomyces Pombe ◽

Gene Disruption ◽

Structure And Function ◽

Biosynthetic Enzyme ◽

Gene Encoding ◽

Complementation Groups ◽

Eukaryotic Organisms ◽

And Function

Abstract The isolation of mutants of Schizosaccharomyces pombe defective in the synthesis of phosphatidylcholine via the methylation of phosphatidylethanolamine is reported. These mutants are choline auxotrophs and fall into two unlinked complementation groups, cho1 and cho2. We also report the analysis of the cho1+ gene, the first structural gene encoding a phospholipid biosynthetic enzyme from S. pombe to be cloned and characterized. The cho1+ gene disruption mutant (cho1Δ) is viable if choline is supplied and resembles the cho1 mutants isolated after mutagenesis. Sequence analysis of the cho1+ gene indicates that it encodes a protein closely related to phospholipid methyltransferases from Saccharomyces cerevisiae and rat. Phospholipid methyltransferases encoded by a rat liver cDNA and the S. cerevisiae OPI3 gene are both able to complement the choline auxotrophy of the S. pombe cho1 mutants. These results suggest that both the structure and function of the phospholipid N-methyltransferases are broadly conserved among eukaryotic organisms.

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