Irvin T R, Wogan G N
Cancer Res. 1985 Aug;45(8):3497-502.
We have examined the time course and patterns of covalent aflatoxin B1:DNA adducts produced within the ribosomal RNA gene sequences isolated from the liver nuclear DNA of aflatoxin B1-treated animals. Liver nuclear DNA was initially enriched in ribosomal DNA by cesium salt density centrifugation, and incubated under alkaline conditions to stabilize bound aflatoxin B1-DNA moieties. Alkali-treated DNA was hybridized to 18S and 28S rRNA, and the RNA:DNA hybrids were recovered by cesium chloride centrifugation. Ribosomal DNA sequences within nuclear DNA were found to be preferential targets for aflatoxin B1 modification. Over a 12-h period after administration of 1-mg [3H]aflatoxin B1/kg dose ribosomal DNA contained 4 to 5 times more aflatoxin B1 residues per mg DNA than did total nuclear DNA. Aflatoxin B1 residues bound to ribosomal DNA were also found to be removed more rapidly than from total nuclear DNA by a factor of 5.7 over the 12-h period postdosing. Levels of the principal aflatoxin B1 adduct, 2,3-dihydro-3-hydroxy(N7-guanyl)aflatoxin B1, as well as the stable formamidopyrimidine derivatives of the parent adduct were also determined. Nuclear DNA isolates were heated to induce depurination of the principal N7-guanine adduct, and differences in adduct levels between alkali-treated (stabilized) and depurinated DNA samples were taken as an approximation of initial levels of this aflatoxin B1:DNA moiety in ribosomal isolates. No differences in the proportions of these aflatoxin B1:DNA adduct species were found in ribosomal as compared to total nuclear DNA, and we conclude that the preferential formation and removal of aflatoxin B1:DNA moieties within ribosomal DNA is not associated with a pattern of adducts qualitatively different from that in total nuclear DNA.
我们研究了从经黄曲霉毒素B1处理的动物肝脏核DNA中分离出的核糖体RNA基因序列内产生的共价黄曲霉毒素B1:DNA加合物的时间进程和模式。肝脏核DNA最初通过铯盐密度离心法富集核糖体DNA，并在碱性条件下孵育以稳定结合的黄曲霉毒素B1-DNA部分。碱处理后的DNA与18S和28S rRNA杂交，通过氯化铯离心回收RNA:DNA杂交体。发现核DNA中的核糖体DNA序列是黄曲霉毒素B1修饰的优先靶点。在给予1mg[3H]黄曲霉毒素B1/kg剂量后的12小时内，每毫克DNA中核糖体DNA含有的黄曲霉毒素B1残基比总核DNA多4至5倍。还发现与核糖体DNA结合的黄曲霉毒素B1残基在给药后12小时内比从总核DNA中去除的速度快5.7倍。还测定了主要黄曲霉毒素B1加合物2,3-二氢-3-羟基（N7-鸟嘌呤基）黄曲霉毒素B1以及母体加合物的稳定甲酰胺嘧啶衍生物的水平。将核DNA分离物加热以诱导主要N7-鸟嘌呤加合物的脱嘌呤作用，碱处理（稳定化）和脱嘌呤DNA样品之间加合物水平的差异被视为核糖体分离物中该黄曲霉毒素B1:DNA部分初始水平的近似值。与总核DNA相比，在核糖体中未发现这些黄曲霉毒素B1:DNA加合物种类的比例存在差异，我们得出结论，核糖体DNA内黄曲霉毒素B1:DNA部分的优先形成和去除与加合物模式在质量上与总核DNA中的模式不同无关。
