Stimulation of sister chromatid exchanges and mutation by aflatoxin B1-DNA adducts in Saccharomyces cerevisiae requires MEC1 (ATR), RAD53, and DUN1.
The hepatocarcinogen aflatoxin B(1) (AFB(1)) is a potent recombinagen but weak mutagen in the yeast Saccharomyces cerevisiae. AFB(1) exposure induces DNA damage-inducible genes, such as RAD51 and those encoding ribonucleotide reductase (RNR), through a MEC1 (ATR homolog)-dependent pathway. Previous studies have indicated that MEC1 is required for both AFB(1)-associated recombination and mutation, and suggested that AFB(1)-DNA adducts are common substrates for recombination and mutagenesis. However, little is known about the downstream effectors of MEC1 required for genotoxic events associated with AFB(1) exposure. Here we show that AFB(1) exposure increases frequencies of RAD51-dependent unequal sister chromatid exchange (SCE) and activates Rad53 (CHK2). We found that MEC1, RAD53, and DUN1 are required for both AFB(1)-associated mutation and SCE. Deletion of SML1, which encodes an inhibitor of RNR, did not suppress the DUN1-dependent requirement for AFB(1)-associated genetic events, indicating that higher dNTP levels could not suppress the dun1 phenotype. We identified AFB(1)-DNA adducts and show that approximately the same number of adducts are obtained in both wild type and rad53 mutants. Since DUN1 is not required for UV-associated mutation and recombination, these studies define a distinct role for DUN1 in AFB(1)-associated mutagenesis and recombination. We speculate that AFB(1)-associated DNA adducts stall DNA replication, a consequence of which can either be mutation or recombination.
Fasullo
Michael
M
Ordway Research Institute, Center for Medical Sciences, Department of Biomedical Sciences, State University of New York at Albany, 150 New Scotland Avenue, Albany, New York 12209, USA.
Sun
Mingzeng
M
Egner
Patricia
P
D016604:Aflatoxin B1 / Q000494:pharmacology*; D006528:Carcinoma, Hepatocellular / Q000139:chemically induced / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000378:metabolism*; D064447:Checkpoint Kinase 2; D019388:Cytochrome P-450 CYP1A2 / Q000737:chemistry; D018736:DNA Adducts; D004261:DNA Replication; D047908:Intracellular Signaling Peptides and Proteins; D009153:Mutagens; D009154:Mutation; D010641:Phenotype; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000187:drug effects* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D012854:Sister Chromatid Exchange; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods; D014466:Ultraviolet Rays
D018797:Cell Cycle Proteins; D018736:DNA Adducts; D047908:Intracellular Signaling Peptides and Proteins; D009153:Mutagens; D029701:Saccharomyces cerevisiae Proteins; D016604:Aflatoxin B1; D019388:Cytochrome P-450 CYP1A2; D011494:Protein Kinases; C104169:DUN1 protein, S cerevisiae; D064447:Checkpoint Kinase 2; C088937:MEC1 protein, S cerevisiae; D017346:Protein Serine-Threonine Kinases; C067022:RAD53 protein, S cerevisiae