RESUMO
Genome stability depends upon the RecQ helicases, which are conserved from bacteria to man, but little is known about how their myriad activities are regulated. Fission yeast lacking the telomere protein Taz1 (mammalian TRF1/TRF2 ortholog) lose many hallmarks of telomeres, including accurate replication and local protection from DNA repair reactions. Here we show that the RecQ homolog, Rqh1, is sumoylated. Surprisingly, Rqh1 acts on taz1Delta telomeres in a deleterious way, promoting telomere breakage and entanglement. Mutation of Rqh1 sumoylation sites rescues taz1Delta cells from these hazards without dramatically affecting nontelomeric Rqh1 functions. The prominence of Rqh1 in the etiology of several different telomere defects supports the idea that they originate from a common underlying lesion--aberrant processing of the stalled telomeric replication forks that accumulate in the absence of Taz1. Our work underscores the principle that RecQ helicases are "double-edged swords" whose activity, while necessary for maintaining genome-wide stability, must be vigilantly controlled.
Assuntos
DNA Helicases/metabolismo , Regulação Fúngica da Expressão Gênica , Processamento de Proteína Pós-Traducional , RecQ Helicases/metabolismo , Proteínas de Schizosaccharomyces pombe/metabolismo , Schizosaccharomyces/enzimologia , Proteínas Modificadoras Pequenas Relacionadas à Ubiquitina/metabolismo , Telômero/metabolismo , Alelos , Temperatura Baixa , DNA Helicases/genética , Replicação do DNA , Regulação Fúngica da Expressão Gênica/efeitos da radiação , Instabilidade Genômica , Genótipo , Mutação , Fenótipo , RecQ Helicases/genética , Recombinação Genética , Origem de Replicação , Schizosaccharomyces/genética , Schizosaccharomyces/crescimento & desenvolvimento , Proteínas de Schizosaccharomyces pombe/genética , Proteínas de Schizosaccharomyces pombe/efeitos da radiação , Estresse Fisiológico/genética , Proteínas de Ligação a Telômeros/deficiência , Proteínas de Ligação a Telômeros/genética , Fatores de TempoRESUMO
Cdt1 is an essential protein required for licensing of replication origins. Here, we show that in Schizosaccharomyces pombe, Cdt1 is proteolysed in M and G1 phases in response to DNA damage and that this mechanism seems to be conserved from yeast to Metazoa. This degradation does not require Rad3 and Cds1, indicating that it is independent of classic DNA damage and replication checkpoint pathways. Damage-induced degradation of Cdt1 is dependent on Cdt2 and Ddb1, which are components of a Cul4 ubiquitin ligase. We also show that Cdt2 and Ddb1 are needed for cell-cycle changes in Cdt1 levels in the absence of DNA damage. Cdt2 and Ddb1 have been shown to be involved in the degradation of the Spd1 inhibitor of ribonucleotide reductase after DNA damage, and we speculate that Cdt1 downregulation might contribute to genome stability by reducing demand on dNTP pools during DNA repair.
Assuntos
Proteínas Adaptadoras de Transdução de Sinal/fisiologia , Proteínas de Ciclo Celular/metabolismo , Proteínas de Ligação a DNA/metabolismo , Proteínas de Ligação a DNA/fisiologia , Proteínas de Schizosaccharomyces pombe/fisiologia , Schizosaccharomyces/metabolismo , Proteínas Adaptadoras de Transdução de Sinal/genética , Ciclo Celular , Proteínas de Ciclo Celular/genética , Proteínas de Ciclo Celular/fisiologia , Proteínas de Ciclo Celular/efeitos da radiação , Quinase do Ponto de Checagem 2 , Dano ao DNA , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/efeitos da radiação , Hidrólise , Proteínas Quinases/genética , Proteínas Quinases/fisiologia , Proteínas de Schizosaccharomyces pombe/genética , Proteínas de Schizosaccharomyces pombe/metabolismo , Proteínas de Schizosaccharomyces pombe/efeitos da radiação , Transdução de SinaisRESUMO
Homologous recombination is an important biological process that occurs in all organisms and facilitates genome rearrangements and repair of DNA double-strand breaks. Eukaryotic Rad51 proteins (Rad51sp or Rhp51 in fission yeast) are functional and structural homologs of bacterial RecA protein, an evolutionarily conserved protein that plays a key role in homologous pairing and strand exchange between homologous DNA molecules in vitro. Here we show that the fission yeast swi5+ gene, which was originally identified as a gene required for normal mating-type switching, encodes a protein conserved among eukaryotes and is involved in a previously uncharacterized Rhp51 (Rad51sp)-dependent recombination repair pathway that does not require the Rhp55/57 (Rad55/57sp) function. Protein interactions with both Swi5 and Rhp51 were found to be mediated by a domain common to Swi2 and Sfr1 (Swi five-dependent recombination repair protein 1, a previously uncharacterized protein with sequence similarity to the C-terminal part of Swi2). Genetic epistasis analyses suggest that the Swi5-Sfr1-Rhp51 interactions function specifically in DNA recombination repair, whereas the Swi5-Swi2-Rhp51 interactions may function, together with chromodomain protein Swi6 (HP1 homolog), in mating-type switching.