Mutational properties of the primary aflatoxin B1-DNA adduct.
The mutagenic activity of the major DNA adduct formed by the liver carcinogen aflatoxin B1 (AFB1) was investigated in vivo. An oligonucleotide containing a single 8,9-dihydro-8-(N7-guanyl)-9-hydroxyaflatoxin B1 (AFB1-N7-Gua) adduct was inserted into the single-stranded genome of bacteriophage M13. Replication in SOS-induced Escherichia coli yielded a mutation frequency for AFB1-N7-Gua of 4%. The predominant mutation was G --> T, identical to the principal mutation in human liver tumors believed to be induced by aflatoxin. The G --> T mutations of AFB1-N7-Gua, unlike those (if the AFB1-N7-Gua-derived apurinic site, were much more strongly dependent on MucAB than UmuDC, a pattern matching that in intact cells treated with the toxin. It is concluded that the AFB1-N7-Gua adduct, and not the apurinic site, has genetic requirements for mutagenesis that best explain mutations in aflatoxin-treated cells. While most mutations were targeted to the site of the lesion, a significant fraction (13%) occurred at the base 5' to the modified guanine. In contrast, the apurinic site-containing genome gave rise only to targeted mutations. The mutational asymmetry observed for AFB1-N7-Gua is consistent with structural models indicating that the aflatoxin moiety of the aflatoxin guanine adduct is covalently intercalated on the 5' face of the guanine residue. These results suggest a molecular mechanism that could explain an important step in the carcinogenicity of aflatoxin B1.
Bailey
E A
EA
Department of Chemistry, Whitaker College of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, 02139, USA.
Iyer
R S
RS
Stone
M P
MP
Harris
T M
TM
Essigmann
J M
JM
D016604:Aflatoxin B1 / Q000009:adverse effects / Q000031:analogs & derivatives* / Q000737:chemistry / Q000633:toxicity*; D017104:Bacteriophage M13 / Q000235:genetics*; D001483:Base Sequence; D006528:Carcinoma, Hepatocellular / Q000139:chemically induced; D018736:DNA Adducts / Q000633:toxicity*; D004279:DNA, Viral / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics / Q000821:virology; D006147:Guanine / Q000031:analogs & derivatives* / Q000633:toxicity; D006801:Humans; D008113:Liver Neoplasms / Q000139:chemically induced; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016296:Mutagenesis; D013014:SOS Response, Genetics; D013329:Structure-Activity Relationship
D018736:DNA Adducts; D004279:DNA, Viral; C072611:aflatoxin B1-DNA adduct; D006147:Guanine; C028319:2,3-dihydro-2-(N(7)-guanyl)-3-hydroxyaflatoxin B1; D016604:Aflatoxin B1