Radiosensitive and Mitotic Recombination Phenotypes of the Saccharomyces cerevisiae dun1 Mutant Defective in DNA Damage-Inducible Gene Expression

Abstract

The biological significance of DNA damage-induced gene expression in conferring resistance to DNA-damaging agents is unclear. We investigated the role of DUN1-mediated, DNA damage-inducible gene expression in conferring radiation resistance in Saccharomyces cerevisiae. The DUN1 gene was assigned to the RAD3 epistasis group by quantitating the radiation sensitivities of dun1, rad52, rad1, rad9, rad18 single and double mutants, and of the dun1 rad9 rad52 triple mutant. The dun1 and rad52 single mutants were similar in terms of UV sensitivities; however, the dun1 rad52 double mutant exhibited a synergistic decrease in UV resistance. Both spontaneous intrachromosomal and heteroallelic gene conversion events between two ade2 alleles were enhanced in dun1 mutants, compared to DUN1 strains, and elevated recombination was dependent on RAD52 but not RAD1 gene function. Spontaneous sister chromatid exchange (SCE), as monitored between truncated his3 fragments, was not enhanced in dun1 mutants, but UV-induced SCE and heteroallelic recombination were enhanced. Ionizing radiation and methyl methanesulfonate (MMS)-induced DNA damage did not exhibit greater recombinogenicity in the dun1 mutant compared to the DUN1 strain. We suggest that one function of DUN1-mediated DNA damage-induced gene expression is to channel the repair of UV damage into a nonrecombinogenic repair pathway.

Srs2 DNA helicase is involved in checkpoint response and its regulation requires a functional Mec1-dependent pathway and Cdk1 activity

“…Dun1-dependent Srs2 phosphoryl-ation might be explained in view of recent results that have pointed out a role for Dun1 in channelling DNA repair into a non-recombinogenic pathway (Fasullo et al, 1999). Since Srs2 plays a similar role (Aboussekhra et al, 1989), it has been suggested that the higher rate of mitotic recombination observed in Ddun1 mutants might result from the inability to phosphorylate speci®c repair proteins, such as the Srs2 helicase (Fasullo et al, 1999). Although we cannot exclude the possibility that Srs2 is a direct substrate of Dun1, we would like to suggest that the pathway dependent upon Mec1, Rad53 and possibly Dun1 acts to modulate Cdk1, which, either directly or indirectly, would cause Srs2 phosphorylation.…”

“…Dun1 has been placed downstream of Rad53 (Zhou and Elledge, 1993) and our data indicate that Srs2 phosphorylation is abolished in Ddun1 mutant cells. Dun1-dependent Srs2 phosphoryl-ation might be explained in view of recent results that have pointed out a role for Dun1 in channelling DNA repair into a non-recombinogenic pathway (Fasullo et al, 1999). Since Srs2 plays a similar role (Aboussekhra et al, 1989), it has been suggested that the higher rate of mitotic recombination observed in Ddun1 mutants might result from the inability to phosphorylate speci®c repair proteins, such as the Srs2 helicase (Fasullo et al, 1999).…”

“…The genotypes of the strains used are listed in Table I. Strains CY2715, CY2835, CY2827, CY2837, CY3138, CY2829 and CY2830 were originated by integrating a Pst I‐linearized pG36 plasmid at the SRS2 locus in strains K699, DMP2541/8A (Paciotti et al ., 1998), DMP2161/25B (Paciotti et al ., 1998), CY2034 (Pellicioli et al ., 1999), YA145 (Fasullo et al ., 1999), K5247 and K5248 (kindly provided by K.Nasmyth), respectively, and by selecting for 5‐FOA‐resistant cells. Correct HA‐SRS2 integration was controlled by Southern analysis.…”

“…Rad53 is also required for phosphorylation of Dun1, another protein kinase involved in the checkpoint response (Zhou and Elledge, 1993; Gardner et al ., 1999). Dun1 plays a major role in the transcriptional induction of several DNA metabolism genes in response to genotoxic treatments (Zhou and Elledge, 1993) and in channelling DNA repair into a non‐recombinational pathway (Fasullo et al ., 1999).…”

Sml1p Is a Dimer in Solution: Characterization of Denaturation and Renaturation of Recombinant Sml1p

“…Eukaryotic cells have evolved multiple strategies to tolerate genomic damage. These include DNA repair systems that remove or bypass potential mutagenic DNA lesions ( , ) and cell cycle delays at multiple transition points after exposure to DNA damaging agents ( − ). Weinert and Hartwell () first observed the control of these delays in budding yeast and called them DNA checkpoints.…”