RESUMO
Several human neurodegenerative diseases result from expansion of CTG/CAG or CGG/CCG triplet repeats. The finding that single-stranded CNG repeats form hairpin-like structures in vitro has led to the hypothesis that DNA secondary structure formation is an important component of the expansion mechanism. We show that single-stranded DNA loops containing 10 CTG/CAG or CGG/CCG repeats are inefficiently repaired during meiotic recombination in Saccharomyces cerevisiae. Comparisons of the repair of DNA loops with palindromic and nonpalindromic sequences suggest that this inefficient repair reflects the ability of these sequences to form hairpin structures in vivo.
Assuntos
Reparo do DNA , DNA Fúngico/química , DNA Fúngico/genética , Conformação de Ácido Nucleico , Saccharomyces cerevisiae/genética , Repetições de Trinucleotídeos , Sequência de Bases , Diploide , Haploidia , Humanos , Meiose , Dados de Sequência Molecular , Doenças Neurodegenerativas/genética , Plasmídeos , Recombinação GenéticaRESUMO
We examined the effect of a single variant repeat on the stability of a 51-base pair (bp) microsatellite (poly GT). We found that the insertion stabilizes the microsatellite about fivefold in wild-type strains. The stabilizing effect of the variant base was also observed in strains with mutations in the DNA mismatch repair genes pms1, msh2 and msh3, indicating that this effect does not require a functional DNA mismatch repair system. Most of the microsatellite alterations in the pms1, msh2 and msh3 strains were additions or deletions of single GT repeats, but about half of the alterations in the wild-type and msh6 strains were large (> 8 bp) deletions or additions.
Assuntos
Repetições de Microssatélites , Polidesoxirribonucleotídeos/genética , Saccharomyces cerevisiae/genética , Sequência de Bases , Reparo do DNA/genética , Replicação do DNA/genética , DNA Fúngico/genética , DNA Polimerase Dirigida por DNA/metabolismo , Dados de Sequência Molecular , Mutação , Plasmídeos/genética , Polidesoxirribonucleotídeos/metabolismo , Análise de Sequência de DNA , Deleção de Sequência/genéticaRESUMO
In mammalian cells, the Ku autoantigen is an end- binding DNA protein required for the repair of DNA breaks [Troelstra, C. and Jaspers, N.G.J. (1994) Curr. Biol., 4, 1149- 1151]. A yeast gene (HDF1) encoding a putative homologue of the 70 kDa subunit of Ku has recently been identified [Feldmann, H. and Winnacker, E. L. (1993) J. Biol. Chem., 268, 12895- 12900]. We find that hdf1 mutant strains have substantially shorter telomeres than wild-type strains. We speculate that Hdf1p may bind the natural ends of the chromosome, in addition to binding to the ends of broken DNA molecules. Strains with both an hdf1 mutation and a mutation in TEL 1 (a gene related to the human ataxia telangiectasia gene) have extremely short telomeres and grow slowly.
Assuntos
Antígenos Nucleares , DNA Helicases , Proteínas de Ligação a DNA/genética , Proteínas Fúngicas/genética , Proteínas Nucleares/genética , Proteínas de Saccharomyces cerevisiae , Saccharomyces cerevisiae/genética , Telômero , Autoantígeno Ku , MutaçãoRESUMO
Yeast chromosomes terminate in tracts of simple repetitive DNA (poly[G1-3T]). Mutations in the gene TEL1 result in shortened telomeres. Sequence analysis of TEL1 indicates that it encodes a very large (322 kDa) protein with amino acid motifs found in phosphatidylinositol/protein kinases. The closest homolog to TEL1 is the human ataxia telangiectasia gene.
